How Does Pigment Red 57:1 Work?

TECHNICAL FIELD The present invention relates to C. I. pigment red 57:1 and a production process thereof, which contains smaller quantities of 3-hydroxy-2-naphthoic acid and a metal salt thereof than those in conventional ones. BACKGROUND ART C. I. pigment red 57:1 is a red pigment containing calcium bis[2-(3-carboxy-2-hydroxynaphthylazo)-5-methylbenzenesulfonate] as an essential component. This C. I. pigment red 57:1 is produced by coupling a diazonium salt of 4-aminotoluene-3-sulfonic acid and 3-hydroxy-2-naphthoic acid to thereby obtain an azo dye, and then laking this azo dye with an inorganic calcium compound (See Patent References 1 and 2). The reaction ratio in obtaining a diazonium salt of 4-aminotoluene-3-sulfonic acid is 98% or more, and is almost stoichiometrically determined regardless of agitating efficiency and the performance of an agitator. Therefore, the molar ratio of a diazonium salt of 4-aminotoluene-3-sulfonic acid and 3-hydroxy-2-naphthoic acid, which are supplied as raw materials to obtain an azo dye, can be described as 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid (molar ratio). Although the stoichiometric molar ratio of the both compounds is 1:1 in the coupling reaction, in consideration of agitating efficiency, the performance of an agitator, and the reaction ratio of a coupler and a base, it has been general to supply raw materials so that the actual molar ratio of 3-hydroxy-2-naphthoic acid exceeds the stoichiometric one by 0.7 to 5 mol %. However, the present inventors have found that the unreacted 3-hydroxy-2-naphthoic acid remains in an azo dye despite the intention even though the reaction is conducted by supplying the raw materials in the aforementioned manner. In C. I. pigment red 57:1 obtained by laking without knowing the remaining 3-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid and metal salts thereof are naturally contaminated as impurities at relatively high concentrations, and these impurities are hard to be removed by washing, etc. Moreover, 3-hydroxy-2-naphthoic acid is produced when metal salts of 3-hydroxy-2-naphthoic acid are contacted with a strong acid for some reasons. Recently, the 3-hydroxy-2-naphthoic acid have been recognized as a chemical compound having mutagenicity, and for example, a guideline for preventing a health problem on exposure to it has been published in the work in which a customer, etc. deals with it. Accordingly, the extinction or the concentration reduction of free 3-hydroxy-2-naphthoic acid begins to be expected. In specific, it is desired that 3-hydroxy-2-naphthoic acid and salts thereof are not eluted to a waste solution, for example in the case where a base ink for a printing ink is prepared by flushing of a pigment press-cake of C. I. pigment red 57:1 with a varnish. In a large-scale production of a pigment itself, from the viewpoint of the security of working environment, it is desired that 3-hydroxy-2-naphthoic acid and salts thereof are not flowed out from C. I. pigment red 57:1 as a waste solution when raw materials are supplied, when an azo dye is produced by the coupling reaction as an intermediate, and when an effluent treatment is conducted in the stage before being provided for a customer. [Patent Reference 1] Japanese Unexamined Patent Application, First Publication No. - [Patent Reference 2] Japanese Unexamined Patent Application, First Publication No. - DISCLOSURE OF INVENTION An object of the present invention it to provide C. I. pigment red 57:1 and a production process thereof, which contains smaller quantities of 3-hydroxy-2-naphthoic acid and metal salts thereof than those in conventional ones and offers high safety of working environment. The present inventors had intensively investigated the process that does not allow 3-hydroxy-2-naphthoic acid and metal salts thereof to remain in C. I. pigment red 57:1 of a final product to be sold for a customer as much as possible in order to contribute to the prevention of a health problem on exposure for a worker dealing with the pigment. As a result, the present inventors discovered that by suppressing the excess percentage of 3-hydroxy-2-naphthoic acid in comparison with conventional ones and conducting agitating so that 3-hydroxy-2-naphthoic acid is consumed at 100% or as a close percentage to 100% as possible, the drawbacks associated with the conventional technology described above could be resolved, and C. I. pigment red 57:1 can be provided, which contains 3-hydroxy-2-naphthoic acid at only a lower level than that in conventional ones. Therefore, the present inventors were able to complete the present invention. In other words, the present invention provides C. I. pigment red 57:1, wherein the total content of 3-hydroxy-2-naphthoic acid and a metal salt thereof, which is measured by quantitative analysis using liquid chromatography, is 2,500 ppm or less as converted into the 3-hydroxy-2-naphthoic acid. In addition, the present invention provides a process for producing C. I. pigment red 57:1 that include: conducting coupling of a diazonium salt of 4-aminotoluene-3-sulfonic acid and 3-hydroxy-2-naphthoic acid; and conducting laking with an inorganic calcium compound, wherein the molar ratio of the 4-aminotoluene-3-sulfonic acid: the 3-hydroxy-2-naphthoic acid is set within a range of 1.000:1.000 to 1.000:1.006, and the coupling is conducted by agitating so that the reaction ratio of the 3-hydroxy-2-naphthoic acid reaches 98.45% or more. According to C. I. pigment red 57:1 of the present invention, the total content of 3-hydroxy-2-naphthoic acid and metal salts thereof, which is measured by quantitative analysis using liquid chromatography, is at a lower level than that in conventional ones, and therefore, the particularly significant effect can be obtained in that safety of working environment in which a customer deals with it is much high. According to a process for producing C. I. pigment red 57:1 of the present invention, the particularly significant effects can be obtained in that the used quantity of 3-hydroxy-2-naphthoic acid that act as the raw material can be reduced by comparison at the same yield and that the pigment can be provided, which offers high safety of working environment in which a customer deals with it is much higher. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an agitator used in Examples 1 to 3. FIG. 2 is a side view of an agitating used in Comparative Example 1. The reference numerals shown in these figures are defined as follows: 1 represents a rotational axis; 2 represents a bottom paddle; 3 represents a paddle; 4 represents a scraper; 5 represents an agitating tank; 20 represents a main agitating blade; and 30 represents an auxiliary agitating blade. BEST MODE FOR CARRYING OUT THE INVENTION A more detailed description of the present invention is provided below. C. I. pigment red 57:1 of the present invention is characterized in that the total content of 3-hydroxy-2-naphthoic acid and metal salts thereof, which is measured by quantitative analysis using liquid chromatography, is 2,500 ppm or less, and preferably 1,000 ppm or less, as converted into the 3-hydroxy-2-naphthoic acid. The term “2,500 ppm or less” means 0 to 2,500 ppm, and the term “1,000 ppm or less” means 0 to 1,000 ppm. The optimal range is 100 to 1,000 ppm. In the present invention, the total content of 3-hydroxy-2-naphthoic acid and the metal salts of 3-hydroxy-2-naphthoic acid and metals such as Ca1/2+, Sr1/2+, Na+, and Al1/3+ is described as the content in the case where all the metal salts are assumed to be 3-hydroxy-2-naphthoic acid. The quantitative analysis using liquid chromatography is abbreviated as liquid chromatography mass spectrometry, and the method thereof is described below. In C.I. pigment red 57:1 of the present invention, rosins can be included according to need. By including rosins in a pigment of the present invention, printability can be much improved when the pigment was used for preparation of printing ink. Herein, as rosins, any conventional one can be used, and examples thereof include a rosin containing abietic acid as a main component, a disproportionated rosin, a partially hydrogenated rosin, a completely hydrogenated rosin, a maleic acid-modified rosin, a fumaric acid-modified rosin, and a polymerized rosin. Rosins can be included at 3 to 30 parts, and preferably 5 to 25 parts per 100 parts by mass of calcium bis[2-(3-carboxy-2-hydroxynaphthylazo)-5-methylbenzenesulfonate]. In the present invention, as the content of 3-hydroxy-2-naphthoic acid in C. I. pigment red 57:1 is lower within a range of 2,500 ppm or less, a health problem on exposure for a worker dealing with the pigment can be prevented more. In addition, by not allowing 3-hydroxy-2-naphthoic acid and metal salts thereof to remain in C. I. pigment red 57:1 of a final product to be sold for a customer as much as possible, the safety of working environment in which a customer deals with the pigment can be much improved. An azo dye prior to the laking of C. I. pigment red 57:1 is produced by reacting a diazonium salt of 4-aminotoluene-3-sulfonic acid that acts as a diazo component, and 3-hydroxy-2-naphthoic acid that acts as a coupler component. In order that the total content of 3-hydroxy-2-naphthoic acid and metal salts thereof, which is measured by quantitative analysis using liquid chromatography, is reduced to 2,500 ppm or less as converted into the 3-hydroxy-2-naphthoic acid, it is preferable not to reduce 3-hydroxy-2-naphthoic acid and metal salts thereof after the pigment production, which is a symptomatic treatment and give only an insufficient effect despite a lot of workloads, but to reduce 3-hydroxy-2-naphthoic acid and metal salts thereof in the step before the pigment production. For this reason, it is preferable that the molar ratio of a coupler component, which is conventionally supplied in large excess, be as close to the stoichiometric molar ratio as possible and that a coupler component be stirred and reacted so that the reaction ratio thereof be as close to 100% as possible in order not to allow an unreacted coupler component to remain. C. I. pigment red 57:1 of the present invention can be produced by conducting coupling of a diazonium salt of 4-aminotoluene-3-sulfonic acid and 3-hydroxy-2-naphthoic acid; and conducting laking it with an inorganic calcium compound, in which the molar ratio of the 4-aminotoluene-3-sulfonic acid: the 3-hydroxy-2-naphthoic acid is set within a range of 1.000:1.000 to 1.000:1.006, and the coupling is conducted by agitating so that the reaction ratio of the 3-hydroxy-2-naphthoic acid reaches 98.45% or more. As described above, in the present invention, the used quantity of 3-hydroxy-2-naphthoic acid is reduced more than before by using the molar ratio of 3-hydroxy-2-naphthoic acid supplied as a coupler component of the raw materials, which is much closer to the stoichiometric molar ratio than before as indicated by 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid (molar ratio)=1.000:1.000 to 1.000:1.006, and the reaction is conducted by agitating so that the reaction ratio of 3-hydroxy-2-naphthoic acid reaches as a high value as 98.45% or more, thereby not allowing 3-hydroxy-2-naphthoic acid of an unreacted raw material to remain in the product after the coupling reaction. In the present invention, the used quantity of 3-hydroxy-2-naphthoic acid can be reduced in the step of supplying raw materials. Therefore, when the same quantity of 3-hydroxy-2-naphthoic acid is used in an industrially large-scale production, a larger quantity of C. I. pigment red 57:1 can be produced than before, and the big contribution to the cost reduction of the pigment can be also expected. The nature of the agitating blade provided within the agitator, which is used for conducting the agitating and mixing of liquid during the coupling reaction in the production of the azo dye that functions as a precursor to the azo lake pigment, tends to be determined independently by each manufacturer on a trial and error basis, and public documents that reveal specific structures are essentially unknown. Examples of the agitating blades provided within the agitator used during the coupling reaction include anchor blades, turbine blades, paddle blades, Pfaudler blades, Maxblend blades (SHI Mechanical & Equipment Inc.), and Fullzone blades (Kobelco Eco-Solutions Co., Ltd.). However, in terms of agitating with less energy consumption, the following agitator is most preferable: an agitator that has a rotational axis fitted with a main agitating blade and an auxiliary agitating blade inside an agitating tank, in which the main agitating blade has tips that are separated from the inner wall surface of the agitating tank so as to generate a rising liquid current during agitating, and is positioned at the lowest point on the central axis, whereas the auxiliary agitating blade has scrapers close to the inner wall of the agitating tank that are either arranged vertically, or inclined so as to push the liquid up during rotation, and has paddles that are connected to the scrapers and are either arranged vertically, or inclined so as to push the liquid down during rotation, and vertically adjacent agitating blades are positioned so that the top edge of the lower agitating blade exhibits a phase lag relative to the bottom edge of the upper agitating blade in the opposite direction to the direction of rotation of the rotational axis. In the present invention, the central axis refers to the rotational axis. When the coupling reaction is conducted using the aforementioned specific agitator, the reaction may be conducted by selecting the conditions under which 98.45% or more of the supplied 3-hydroxy-2-naphthoic acid are reacted. In specific, by agitating at a required power of at least 0.1 but less than 1.0 kW/m3, for a period of 5 to 60 minutes, 98.45% or more of the supplied 3-hydroxy-2-naphthoic acid can be reacted. According to the coupling reaction method using the aforementioned specific agitator, in comparison with the methods using other conventional agitators, the energy consumption described as the product of a required power and a time period can be much suppressed, and therefore, the productivity of the pigment is much improved at the same energy consumption. The reaction ratio of 3-hydroxy-2-naphthoic acid refers to the reaction ratio which is obtained by the quantity of the 3-hydroxy-2-naphthoic acid consumed by the reaction with a diazonium salt of 4-aminotoluene-3-sulfonic acid per the quantity of the supplied 3-hydroxy-2-naphthoic acid. In C.I. pigment red 57:1, the pigment slurry prior to drying is turned into an object according to the measurement of the total content of 3-hydroxy-2-naphthoic acid and the metal salts thereof by using the quantitative analysis using liquid chromatography, and the reaction ratio is calculated by liquid chromatography mass spectrometry of 3-hydroxy-2-naphthoic acid. The diazo component may be a diazonium salt of 4-aminotoluene-3-sulfonic acid alone, but diazonium salts of other aromatic amines including isomers and derivatives of the aforementioned aromatic amines such as 1-amino-4-methylbenzene-3-sulfonic acid and tobias acid can be included within 15 mol % of the diazo component. Conventional processes can be used to obtain 4-aminotoluene-3-sulfonic acid and diazonium salts of other aromatic amines, and the reaction ratio (hereinafter, referred to as a diazotization ratio) is 98% or more. The coupler component is also most preferably 3-hydroxy-2-naphthoic acid alone, but phenols and naphthols such as 2-hydroxynaphthalene can be included within 15 mol % of the coupler component. Any conventional process can be used to obtain the corresponding aqueous solution from the coupler component, and for example, the aforementioned component may be dispersed in heated water so as to be dissolved as an alkaline. The reaction temperature of the coupling is not restricted, but is conventionally within a range of 0° C. to 60° C., and preferably within a range of 0° C. to 40° C. Meanwhile, the laking reaction is conducted by adding an inorganic calcium compound at the quantity corresponding to the total equivalent quantity of the sulfonic acid group, the carboxyl group, and the water-soluble salts thereof in an azo dye. In this case, from the viewpoint of the reaction ratio, etc., the aforementioned quantity can be adjusted. Calcium is a divalent metal, and therefore, in the laking reaction of the azo dye that includes two monovalent acid groups in the molecule, 1 mol of an inorganic calcium compound is stoichiometrically used for 1 mol of the azo dye. The reaction temperature of the laking is not restricted, but is conventionally within a range of 0° C. to 60° C., and preferably within a range of 0° C. to 40° C. As an inorganic calcium compound, calcium chloride can be used, for example. The suspension including the laked pigment can be used as a pigment after being directly subjected to filtration and/or drying. Moreover, the suspension can be aged in order to arrange the particle configuration of the pigment following the pH adjustment according to need. Heating is conducted at the temperature of 60 to 90° C. for a period of 30 minutes to 2 hours. In the aforementioned production process of C. I. pigment red 57:1, the aforementioned rosins may be added to the aqueous solution containing a coupler component, or the aqueous solution or the suspension of an azo dye according to need. Rosins can be added at the aforementioned quantity. According to the aforementioned production method, C. I. pigment red 57:1 of the present invention can be easily obtained, in which the total content of 3-hydroxy-2-naphthoic acid and a metal salt thereof, which is measured by liquid chromatography mass spectrometry, is 2,500 ppm or less as converted into the 3-hydroxy-2-naphthoic acid. As for C. I. pigment red 57:1 produced by the process of the present invention, the lower is the total content of 3-hydroxy-2-naphthoic acid and a metal salt thereof measured by quantitative analysis using liquid chromatography, the higher can be the safety of working environment. As for C. I. pigment red 57:1 produced by the process of the present invention, 3-hydroxy-2-naphthoic acid and salts thereof are not flowed out from C. I. pigment red 57:1 as a waste solution when an effluent treatment is conducted in the stage before being provided for a customer. Therefore, the ink can be obtained, which has both of the environmentally-friendly property and the excellent printability which is the same level as before or more. A pigment of the present invention is used for coloring a medium in a wet state or a dry state. As for the pigment aqueous suspending solution of C. I. pigment red 57:1 produced by the process of the present invention, in which the total content of 3-hydroxy-2-naphthoic acid and a metal salt thereof is 2,500 ppm or less as converted into the 3-hydroxy-2-naphthoic acid, wet states of any moisture contents such as a pigment aqueous slurry, a pigment aqueous paste, and a press-cake can be obtained by subjecting the pigment to filtration, etc. so as to reduce the moisture. In the present invention, a pigment aqueous paste refers to a pigment composition including calcium bis[2-(3-carboxy-2-hydroxynaphthylazo)-5-methylbenzenesulfonate] and water, in which the moisture content is within a range of 60 to 80 mass %. As described above, a pigment aqueous paste can be used for the production of an offset ink subjected to flushing. A base ink for an offset ink can be prepared by kneading a varnish for an offset ink containing a binder resin and an organic solvent, and a pigment aqueous paste containing the pigment of the present invention, followed by flushing. As for a pigment of the present invention, 3-hydroxy-2-naphthoic acid and a metal salt thereof are not included, or the total content thereof is largely reduced. Therefore, the environmental load of drainage in the aforementioned flushing is significantly low. The base ink obtained in this manner is mixed with various diluents, additives, curing accelerator, etc., to thereby produce an offset ink. The aforementioned pigment of the present invention in a wet state is dehydrated by conventional methods such as spray-dry, hot-air drying, far infrared rays drying, to thereby prepare a dry state. If necessary, crushing and classification can be further conducted to arrange the particle diameter and the distribution thereof, and then, the pigment may be provided for use. Pigments of the present invention in a wet sate or a dry state can be used for conventional various applications including general-purpose applications such as printing inks including a lithography ink, a gravure printing ink, and a flexographic printing ink, coating agents, and colored plastic molded items; as well as high-tech applications such as electrostatic latent image developing toners, color filters, and inkjet recording aqueous inks. FIG. 1 shows an example of the specific agitator exemplified as an optimal apparatus. Also, FIG. 1 shows an agitator used in Examples described below, wherein an upper blade, a middle blade and a broad bottom paddle 2 are fitted to a rotational axis 1 inside an agitating tank 5. In this FIG. 1, the broad bottom paddle 2 functions as the main agitating blade 20, and the middle blade and upper blade function as auxiliary agitating blades 30. This agitator includes the circular cylindrically shaped agitating tank 5, and a central axis, which is positioned within the center of the tank and is fitted sequentially with the upper blade, the middle blade and the lower bottom paddle 2. The positioning of these blades assumes that the direction of rotation of the central axis is in a clockwise direction when viewed from above. In this configuration, the middle and upper agitating blades each have tips that are separated from the inner wall surface of the agitating tank 5, and a single blade arm is formed from a scraper 4, which is shaped like a letter “T” on its side, and a paddle 3 that is positioned adjacent to the scraper, with each agitating blade formed from a pair of these blade arms. Both of the agitating blades have the scrapers 4 close to the inner wall of the agitating tank 5, in an inclined arrangement that pushes the liquid up during rotation, and have the paddles 3 connected to the scrapers 4 in an inclined arrangement that pushes the liquid down during rotation. Moreover, vertically adjacent agitating blades are positioned so that the top edge of the lower agitating blade exhibits a phase lag of 30° relative to the bottom edge of the upper agitating blade in the opposite direction to the direction of rotation of the rotational axis 1. In FIG. 1, the fact that the middle blade appears larger than the upper blade is intended to reflect the phase difference between the two blades. Both the middle blade and the upper blade are designed such that the ratio of the total length of the agitating blade across the central axis relative to the internal diameter of the agitating tank 5 is 0.85. As the agitating blades are rotated, the scrapers 4 promote the upward movement of the mixture of the diazo component and the coupler component inside the tank, thereby forming a rising liquid current. This rising liquid current changes to a descending liquid current near the central axis. During rotation of the agitating blades, the paddles 3 also promote the downward movement through the center of the tank of the mixture of the diazo component and the coupler component. Configurations in which both the paddles 3 and the scrapers 4 are inclined exhibit superior mixing properties to configurations in which both the paddles 3 and the scrapers 4 are vertical. Moreover, in the apparatus shown in FIG. 1, because the upper blade and the middle blade are arranged with a phase lag therebetween, the mixing properties can be improved compared with the case where agitating is conducted using only a single auxiliary agitating blade. Furthermore, in the bottom paddle 2 at the lower point, the tips of the paddles close to the tank inner wall surface are both bent 45° in the opposite direction to the direction of rotation, thereby reducing the resistance accompanying the agitating. The wide paddle 2 prevents the mixture of the diazo component and the coupler component from accumulating in the lower regions of the agitating tank. In the agitating tank, a flow pattern is formed in which the mixture of the diazo component and the coupler component in the bottom portion of the tank that is stirred by the bottom paddle 2 is pushed up the tank by the actions of the scrapers 4 of the middle blade and the scrapers 4 of the upper blade, whereas the mixture of the diazo component and the coupler component in the upper portion of the tank is pushed down by the paddles 3 of the upper blade and the paddles 3 of the middle blade, and as a result, the mixing of the mixture within the tank is enhanced, and the coupling reaction becomes smoother and more uniform. EXAMPLES A description of specifics of the present invention is provided below using a series of Examples. In the following description, unless stated otherwise, “parts” and “%” refer to mass-referenced values. Measurement Device for Liquid Chromatography Mass Spectrometry: Liquid chromatography mass spectrometry device HP manufactured by Yokogawa Analytical Systems Co., Ltd. was used. Conditions for Liquid Chromatography Mass Spectrometry: 30 mM ammonium acetate aqueous solution and acetonitrile were used as eluants, and ODS column was used as a column. Quantitative Analysis Method of 3-hydroxy-2-naphthoic Acid (BON Acid) in Pigment: 100 mg of the standard sample were weighed with the 50 mL volumetric flask, and dimethylsulfoxide (DMSO) was added thereto so as to adjust the constant volume. The flask was tightly stoppered, and the solution was dissolved by the ultrasonic dispersing machine (manufactured by KAIJO Corporation, Model: C-) for 1 hour. This solution was appropriately diluted to prepare the solution samples for the calibration curve. The above-prepared solution samples with various contents for the calibration curve are injected into the LC measurement device equipped with the aforementioned column and using the aforementioned eluants, which was prepared separately from the Liquid chromatography mass spectrometry device. Then, the peak of 3-hydroxy-2-naphthoic acid (BON acid) was detected at the retention time (Rt.) of 12.3 min, and by measuring the integration value of the peak area of the each solution sample, the calibration curve was preliminarily made for the quantity of the 3-hydroxy-2-naphthoic acid (BON acid). The powder pigment produced by Examples described below was prepared, 5 mg thereof was precisely weighed, and the liquid sample was prepared in the same manner as the aforementioned. This liquid sample was injected into the aforementioned LC measurement device under the same conditions as the aforementioned, and the content (ppm) of 3-hydroxy-2-naphthoic acid (BON acid) in the powder pigment was calculated by an absolute calibration method. Example 1 34.80 parts of 4-aminotoluene-3-sulfonic acid (purity: 98.00%) was dispersed in 50 parts of water, 22.1 parts of 35% hydrochloric acid was added, ice and water were added, and with the temperature held at 0° C., 32.4 parts of a 40% aqueous solution of sodium nitrite was added in a single batch, thereby yielding 650 parts of a suspension containing a diazo component. Next, 34.98 parts of 3-hydroxy-2-naphthoic acid (purity: 98.50%) was dispersed in 400 parts of 50° C. water, 69 parts of a 25% aqueous solution of caustic soda was added and dissolved, and ice and water were then added, thus forming 980 parts of a 10° C. aqueous solution containing a coupler component. The total quantity of this aqueous solution containing the coupler component was placed inside a circular cylindrically shaped agitating tank 5 with an internal capacity of 2 liters, a rotational axis 1 fitted with each of the agitating blades shown in FIG. 1 was positioned within the center of the agitating tank 5, and the rotational axis 1 was then fixed to a motor, thereby completing the setup of the agitator. Subsequently, the rotational axis 1 was rotated at a rotational rate of 100 rpm, and with the aqueous solution containing the coupler component undergoing constant agitating, the total quantity of the aforementioned suspension containing the diazo component was added in a single batch. The reaction temperature was maintained at 10° C. to 15° C. After 10 minutes, completion of the coupling reaction was confirmed using the H acid color test described below. Subsequently, 147 parts of an aqueous solution of a 10% disproportionated rosin sodium salt was added, and following agitating for a further 60 minutes, the pH was adjusted to 12.5, yielding an azo dye suspension. In Example 1, the molar ratio of 4-aminotoluene-3-sulfonic acid: the 3-hydroxy-2-naphthoic acid was set to 1.000:1.005. To the agitating tank 5 containing the azo dye suspension was added 80 parts of a 35% aqueous solution of calcium chloride, and the resulting mixture was stirred for 60 minutes to complete the laking reaction, thus yielding a suspension containing a C.I. Pigment 57:1. This suspension was aged by agitating for 90 minutes at a temperature of 80° C. In both the laking step and the heating step, the rotational rate of the agitating blades was set to the same rate as that used in the coupling reaction, and the coupling reaction, the laking reaction and the heating were conducted consecutively in the same agitating tank 5, with no change of the tank. Ice was then added, the liquid temperature was cooled to 60° C., and hydrochloric acid was used to adjust the pH to a value of 8.5. Subsequently, the product was filtered, washed with water, dried for 10 hours at 100° C., and then pulverized, yielding 93 parts of a dried pigment powder of the C.I. Pigment 57:1. (H Acid Color Test) A dilute aqueous solution of sodium hydroxide containing 1-amino-8-naphthol-3,5-disulfonic acid (H acid) was used as the color test reagent (the reagent for coloring). The point where no coloring occurred upon reaction with the coupling reaction liquid was taken as the end point of the coupling reaction. Example 2 With the exception of setting the molar ratio of 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid (molar ratio) to 1.000:1.002, production was conducted in the same manner as Example 1, yielding 93 parts of a dried pigment powder. Example 3 With the exception of setting the molar ratio of 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid to 1.000:1.003, production was conducted in the same manner as Example 1, yielding 93 parts of a dried pigment powder. Comparative Example 1 The molar ratio of 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid was set to 1.000:1.005, and a suspension containing a diazo component and an aqueous solution containing a coupler component were prepared. The aqueous solution containing the coupler component was added into a circular cylindrically shaped reaction apparatus with an internal capacity of 2 liters and the agitating blades shown in FIG. 2, which was similar to the one in Example 1, and the suspension containing the diazo component was then added thereto while the agitating blades were rotated at a rotational rate of 300 rpm. The reaction temperature was maintained at 10° C. to 15° C. After 60 minutes, the coloring was conducted using the H acid color test, 147 parts of an aqueous solution of a 10% disproportionated rosin sodium salt was added without completion of the coupling reaction, and following agitating for a further 60 minutes, the pH was adjusted to 12.5, yielding an azo dye suspension. The laking and heating were conducted using this azo dye suspension in the same manner as Example 1, yielding 92 parts of a dried pigment powder of the C.I. Pigment 57:1. Herein, FIG. 2 represents the agitator in which the rotational axis 1 a fitted with the lower blade made of the paddle blade 20 a and the upper blade made of the propeller blade 30 a with the same center and diameter as the lower blade is placed inside the agitating tank 5 a. Although cannot be directly shown in FIG. 2 because the phase lag between the paddle blade 20 a and the propeller blade 30 a is 90°, the propeller blade 30 a has a pair of propellers in the upward direction and the downward direction of the drawing, and these propellers are fixed so that they become straight when viewed from above, and can be rotated around the rotational axis 1 a. These propellers are inclined so as to push liquid up during rotation. Each of the diazotization ratios of the 4-aminotoluene-3-sulfonic acid in Examples 1 to 3 and Comparative Example 1 was within a range of 99.0% to 99.2%. The pigment slurries prior to drying and after washing with water in Examples 1 to 3 and Comparative Example 1 were used as samples, and using liquid chromatography mass spectrometry, the reaction ratios of 3-hydroxy-2-naphthoic acid were calculated from the ratio of the consumed 3-hydroxy-2-naphthoic acid/the supplied 3-hydroxy-2-naphthoic acid. Table 1 shows all the conditions of Examples 1 to 3 and Comparative Example 1. The molar ratio of supplied raw materials in Table 1 refers to the molar ratio of 4-aminotoluene-3-sulfonic acid: 3-hydroxy-2-naphthoic acid. TABLE 1 Molar Ratio of Supplied Reaction Ratios of Table 1 Raw Materials 3-hydroxy-2-naphthoic acid (%) Example 1 1.000:1.005 98.51 Example 2 1.000:1.002 98.80 Example 3 1.000:1.003 98.70 Comparative 1.000:1.005 95.52 Example 1 In Examples 1 to 3, the reactions were conducted at a required power within a range from 0.1 to 0.9 kW/m3 for a period of 5 to 30 minutes, and the energy consumption required for the coupling reaction was able to be suppressed at a lower level than that in Comparative Example 1. Moreover, the dried pigment powders obtained in Examples 1 to 3 and Comparative Example 1 were used as samples, and using liquid chromatography mass spectrometry, the contents of 3-hydroxy-2-naphthoic acid and metal salts thereof were measured, and converted into 3-hydroxy-2-naphthoic acid. The results are shown in Table 2. As described above, it is preferable that the total content of 3-hydroxy-2-naphthoic acid and metal salts thereof be 2,500 ppm or less as converted into the 3-hydroxy-2-naphthoic acid, and be as close to 0 ppm as possible. TABLE 1 Contents of 3-hydroxy-2-naphthoic Table 2 Acid and Metal Salts Thereof Example 1 Example 2 798 Example 3 Comparative Example 1 The contents of 3-hydroxy-2-naphthoic acid and metal salts thereof in Examples 1 to 3 were lower than that in Comparative Example 1. Test Example 1 Mixtures containing 6 parts of the each pigment obtained in Examples 1 to 3 and Comparative Example 1, 39 parts of a planographic printing ink vehicle containing a rosin-modified phenolic resin, and 5 parts of light oil were dispersed at 40° C. and a compression pressure of 15 bar using a triple roll mill manufactured by Buhler AG. In specific, firstly, the mixtures were dispersed for 5 minutes using double roll mill, and then passed 3 times through the triple roll mill, thus preparing a series of simulated planographic printing inks (planographic printing inks prior to inclusion of a drier). (Tinting Strength) Light-colored inks were prepared by mixing 0.2 parts of each of the simulated planographic printing inks with 2.0 parts of a white ink (titanium oxide). The tinting strength of each ink was determined using a Gretag apparatus (manufactured by GRETAG Limited). The tinting strength for the simulated planographic printing ink of Comparative Example 1 was deemed to be 100, and the corresponding numerical tinting strengths for the inks of Examples 1 and 2, and Comparative Example 1 are shown in Table 3. Using each of the simulated planographic printing inks, the dispersibility of the pigment within the ink and the transparency of the ink in the printed image were evaluated. The results are shown in Table 3. The method and criteria used for evaluating the dispersibility and transparency are as described below. (Dispersibility) The dispersibility of each of the simulated planographic printing inks was evaluated using a grind gauge. A: very good, B: good, C: fair, D: poor (Transparency) Each of the simulated planographic printing inks was thinly spread on a substrate and dried so as to form a colored, dried film. Then, the transparency of the resulting colored image was evaluated visually. A: very good, B: good, C: fair, D: poor TABLE 3 Tinting Table 3 Strength Transparency Dispersibility Example 1 100 B B Example 2 100 B B Example 3 100 B B Comparative Example 1 98 B B As can be seen in Table 3, C. I. pigment red 57:1 of the present invention exhibited similar tinting strength, transparency and dispersibility to conventional inks, and the total content of 3-hydroxy-2-naphthoic acid and metal salts thereof, which was measured by quantitative analysis using liquid chromatography, at a lower level than that in conventional inks. Therefore, it is clear that safety of working environment in which a customer deals with C. I. pigment red 57:1 of the present invention is much high. Moreover, as can be seen in Table 1, in each of the production methods of C. I. pigment red 57:1 of Examples, while the supplied quantity of 3-hydroxy-2-naphthoic acid of a coupler component was suppressed, the reaction ratio of 3-hydroxy-2-naphthoic acid was increased, and the energy consumption of the agitator was also largely suppressed. Accordingly, it is clear that the pigment, which exhibits similar tinting strength, transparency and dispersibility to conventional inks and high safety of working environment in which a customer deals with it, is obtained at a lower energy consumption than before. INDUSTRIAL APPLICABILITY According to the present invention, the pigment, which exhibits similar tinting strength, transparency and dispersibility to conventional inks and high safety of working environment in which a customer deals with it, can be obtained at a lower energy consumption than before. Accordingly, the present invention is very useful industrially.

Color Index Generic Name:   Key Top ^ Page Top^
This is the C.I. Generic Name (abbreviated) given by the ASTM and Colour Index International (CII) for that pigment. The first 2 or 3 letters describe the general pigment color and the number is the individual pigment identifier. N/A (not applicable) means that pigment has not been given a color index name or number.

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Natural Dye and Solvent Pigments
These are naturally occurring organic pigments and dyes. With a few exceptions, most are plant or animal extracts or dyes that need to be fixed to a substrate to become pigments (i.e. Madder Lake). A few are organic natural earths such as Cassel earth (Van Dyke Brown). They are designated with C.I. Generic name of which consists of the usage class "Natural" and basic hue, followed by the CI serial number (i.e. Natural Brown 8). Natural pigment CI generic names are often abbreviated with the usage class N + the hue abbreviation + the serial number. (i.e. NBr 8) Pigment
Pigments can be organic or Inorganic. Most modern pigments are given this usage designation by the Color Index. They can be completely synthetic, naturally occurring minerals, or lakes based on the synthetic derivatives of natural dyes. Pigments are designated with C.I. Generic name which consists of the usage class "Pigment" and the basic hue followed by the CI serial number (i.e. Pigment Red 106, Cadmium Red). The pigment CI generic names are often abbreviated with the usage class P + the hue abbreviation + the serial number. (i.e. PR83 for Pigment Red 83)

NY = Natural Yellow;
NO = Natural Orange;
NR = Natural Red;
NV = Natural Violet;
NB = Natural Blue;
NG = Natural Green;
NBr = Natural Brown;
NBk = Natural Black;
NW = Natural White;

PY = Pigment Yellow;
PO = Pigment Orange;
PR = Pigment Red;
PV = Pigment Violet;
PB = Pigment Blue;
PG = Pigment Green;
PBr = Pigment Brown;
PBk = Pigment Black;
PW = Pigment White;
PM = Pigment Metal

The CI (Color Index) Common Pigment Name:   Key Top ^ Page Top^
In this database the common name is the name given in the Color Index (third edition, ) by the Color Index International published by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists, and are also used by the ASTM International, American Society for Testing and Materials.

When the Colour Index (3rd edition) has not specified a name, I have used the name that the first manufacturer, inventor or original patent holder has given that pigment. In the case of ancient pigments, historic pigments, minerals or other odd pigments, I have used the most commonly used traditional historic, mineral or chemical name as determined by my research.

Common, Historic and Marketing Names:   Key Top ^ Page Top^

These are the various names that have been used for that pigment whether or not it is the correct usage. This is NOT an endorsement of any particular name, but merely a collection of names that are in common usage or have been used in the past according to historic pigment books & references, paint sales literature, and pigment manufacturers references. They have been collected (in order of importance) from

1.) Paint manufacturers, pigment manufacturers and/or other pigment supplier literature;

2.) Various web sites (an incomplete list, in no particular order): AMIEN.org is unfortunetly gone, but the good news is the MITRA (Materials Information and Technical Resources for Artists) has taken up the cause, Handprint.com; WetCanvas.com; Blick Art Materials Artist Supply Pigment Information; Boston Fine Arts CAMEO Conservation & Art Materials Encyclopedia; Kremer Pigments; Natural Pigments; Kama Pigments; Sinopia Pigments; PCImag.com; WebExhibits.org "Pigments through the Ages Online Museum"; and along with internet forums on art and painting, web sites of paint manufacturers, paint suppliers, chemical manufacturers and pigment manufacturers;

3.) The Color Index, Third edition (published by the Colour Index International, );

4.) Historical books on pigments, oil painting, watercolor painting and other art forms (see Free Art e-Books);

5.) Artist manuals and handbooks (see the bottom of the Pigment Database's main page for a complete list of reference works);

6.) Various dictionaries and encyclopedias (both historic and contemporary, online and physical).

(hue):
When a manufacturer has has used a common historical name for a pigment that is not the accepted traditional historic pigment name and has not clearly indicated it to be a hue or substitute, I have indicated it with the "(hue)"* in parenthesis. For example calling/naming a paint made with Phthalocyanine Blue as "Egyptian Blue", "Smalt" or "Cobalt Blue".

* In order to stay within ASTM specification D -05, manufactures are encouraged to use the word "hue" when the paint or pigment marketing name is not the real name of a paint or a pigment. 'Substitute', 'tone' or prefixed with words like 'Permanent' could be also considered acceptable means of indicating a hue substitute for the actual color. The ASTM specifications are voluntary and no one enforces them. Also because of language differences, changes in the paint or pigments common identification and because of contemporary usage (often perpetrated by manufacturer's incorrect color marketing names), and last but not least - the sheer multitude of historically used paint names for any given paint\pigment, it's nearly impossible to prove or say a manufacturer of art materials is being purposely deceptive.

C.I. Constitution Number or Colour Index Constitution Number (chemical composition):   Key Top ^ Page Top^

These are the chemical constitution numbers given that pigment by the Color Index International published by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists, and are also used by the ASTM International, American Society for Testing and Materials. Each of the numbers in the "Colour Index Constitution Number" has a specific chemical or compositional meaning; for more information see the Colour Index Number Chart or go to the Color Index International and ASTM, American Society for Testing and Materials web sites (these links open in a new window)..

Chemical Composition:   Key Top ^ Page Top^

These are the basic chemical names, or mineral names along with chemical composition and sometimes, when available, manufacturing details. I have also included CAS numbers, when I can fine them. Sometimes multiple names are given because chemical names can be stated in different ways, the different chemical names can be an indication of the different manufacture methods. Very often a pigment can be a group of related compounds rather than one specific chemical. I have not included detailed chemical descriptions or analyses, but only basic information that should help you to find further information. I have included references designated with "(Ref)" where further information can be attained.
Adulterants, extenders and other additives may be added to artistic paints & pigments to improve the paint rheology, transparency, wetting and\or drying time. Often inert pigments, extenders and fillers are added to the color pigments in student grade paints or to modify paint pigments with overly strong tinting strength, i.e. the Phthalocyanine Blues and Greens. These extra ingredients are rarely listed of the label.

Color Description:   Key Top ^ Page Top^

This is a general attempt to explain the color, hue and value in plain English. The perception of color is as individual as the the people viewing it and any such description can not be completely accurate, but merely give a general idea of the what color looks like to the average person. Many pigments have a range of shades and hues. This range in hues, even in the same pigment, can be due to many things such as different manufacturing processes, chemical modifiers added during production, calcining temperature and length of time, milling time, particle size, exact chemical composition, in lake pigments the base the dye is fixed on, additives, binder , etc, etc.. In most cases, i have not used any of the attempted means of standardizing color descriptions for this (such as the Munsell system), but where the pigment is included in the Color Index International Pigments and Solvent Dyes (The Society of Dyers and Colourists, third edition ), I have used that description, when there is no color hue description in the Color Index, I have used other reference sources, in particularly, manufacturer or supplier literature and personal judgement.

† = Effects of long term light exposure are given when known, this may allow an artist to anticipate color changes and possibly use them as an advantage. These effects are all relative to the pigments inherent light fastness and may take decades or even centuries in museum conditions to be visible.

Fades = Loses chroma and becomes more Transparent
Lightens = Loses chroma but maintains relative transparency or opaque character;
Whitens = Becomes lighter towards white and more opaque;
Darkens = Becomes darker but retains hue;
Dulls = Loses chroma towards neutral but maintains the relative tone value;  
Blackens = Becomes darker moving towards black losing chroma;  
Hue shift = Changes hue towards a different color

You will get efficient and thoughtful service from Ogilvy.

Recommended article:
10 Questions You Should to Know about CAS 7790-98-9

Opacity - Transparency:   Key Top ^ Page Top^

This designation is only a general reference to the most common encountered opacity or transparency inherit to the pigment. In paint formulations, the transparency of a pigment can change due to what is used as the painting medium or binder (i.e., oil color, watercolor, encaustic, acrylic, etc.). There are many pigments that are opaque in watercolor but transparent or semi-transparent in oil paints. The transparency of a paint or pigment can often be manipulated by the manufacturing process for a particular purpose and so some pigments are available in transparent and opaque versions. The addition of inert pigments or other modifiers can also change the perceived transparency of a paint formulation or pigment.
When available, i have used the Color index's designation or manufacturers literature to arrive at this figure. When the Color Index description is unavailable i have arrived at a general figure by manufacturer literature or personal experience. A general designation such as given will not always be the case in any particular formulation.
 
1 = Opaque,
2 = Semi-Opaque,
3 = Semi-Transparent,
4 = Transparent

Light Fastness Rating:   Key Top ^ Page Top^

The light fastness ratings can only be a general guide, the only reliable way to confirm lightfastness in your paints and your preferred medium is to make your own tests on the paint brand or pigment you have. I have used the ASTM rating when possible, but The ASTM has not rated all pigments, and stopped rating pigments entirely sometime in the late 90's early 's. The ASTM stopped rating pigments because it is not possible to test every pigment & shade of pigment in every binder and have the results mean anything in the real world. The ASTM now advises that the manufacturer of a brand make their own tests according to the ASTM D-10 guidelines and submit them to the ASTM for approval. However I don't know of any company that has done this. The ASTM lightfastness ratings were never a perfect way to determine light fastness of a pigment that has been used in a unique paint brand formulation.

For the reasons above, the rating in this database, will not always be the official ASTM rating but a rating culled & averaged from other sources such as individual paint brand ratings, my own personal tests, tests results in other sources such as books, artist forums and websites like Handprint.com and/or pigment manufactures literature and blue wool scales. The ASTM ratings have a 5 increment scale and the blue-wool scale is 8, in this database I will use the same scale as the ASTM for light fastness ratings, even though they may not be ASTM ratings. Very often, pigments in tints are less light fast than in full masstone and this should be taken into account when determining if a pigment or paint will meet your needs. ASTM ratings only have a rating for full shade or masstone. I can not cover every possible paint, binder, or pigment formulation in this chart as it would take too much time and space. Many factors can influence the light fastness of any particular paint formulation, for instance, the quality of the actual pigment manufacture and amount & type of impurities has much influence on a pigments fastness to light. Particle size, extenders, binder, and additives play a role in light fastness too. Most artist paint brands and the ASTM do not test for the effects of heat, moisture, pollution or other environmental factors. Whether a paint is watercolor, oil color, tempera, etc. has an effect on light fastness. Varnishes and other treatments to the painting surface or support can have an influence too. As a general rule (but not always the case) oil, alkyd and acrylic binders add some degree of protection and will be slightly more light fast than watercolors.Reference the following: (ASTM D - 10, Standard Test Methods for Lightfastness of Colorants Used in Artists' Materials, or ASTM D01.57, the Subcommittee on Artists' Materials doc here, opens new window);

Blue Wool Scales will be added when found, but be aware that most of these will be tests performed by the pigment manufacturer on a single formulation that could be results from melamine (Plastic), alkyd, oil, water or acrylic emulsions and may not be indicative of it's use in all / or any particular artist paint brand or binder.

ASTM scale or equivalents (see the table below for conversion to & from the Blue Wool Scale):

I = Excellent, should last over 100 years in Museum conditions
II = Very Good, should show no signs of change for 50–100 years in Museum conditions
III = Fair, should show no signs of change for 15–50 years in Museum conditions
IV = Poor, should last 2–15 years in Museum conditions
V = Fugitive or very poor, will show changes in 2 years or less in Museum conditions

BWS = Blue wool scale

7-8 = ASTM I, Excellent
6 = ASTM II, Very Good
4-5 = ASTM III, Fair
2-3 ASTM IV, Poor (Impermanent)
1 = ASTM V, Very Poor (fugitive)*

*When known, blue wool scale ratings will be given for tints in the following format: Full;1/2 tint/;1/4 tint (i.e. Cadmium Red would be 8;8;8 with excellent light fastness in all tints). Note: these may from tests on a single formulation or pigment brand, and may not be valid for other brands or binders.

Oil Absorption: is given in g/100g or grams of oil per 100 grams of pigment   Key Top ^ Page Top^
or as H, M, L (see below)

The oil absorption figure has been arrived at from the pigment manufacturer's literature or artist reference sources (see the bottom of the Pigment Database's main page for a complete list of reference works). The higher the oil absorption, generally, the longer it will take to dry when used in oil painting. The addition of driers, siccatives, retardants and other additives can effect the drying time of any specific formulation, or they can be added by the artist to speed up or slow down the drying of oil paints. In some literature the oil absorption rate is given as ml/100g, although not technically the same as g/100g, for the purposes of this database they are close enough.

Depending on the specifications i have available I may also use the following designations:
H = High;   - These pigments absorb a lot of oil.
M = Medium;    - absorbs a medium amount of oil, and generally will have an average drying or cure rate
L = Low;    - absorbs very little oil, usually very fast driers

Toxicity:   Key Top ^ Page Top^

Under this heading will be a general designation of a possible hazard. It is assumed intelligent people will use at least ordinary care when handling all paints or pigments. An rating of A in this database does not mean the pigment is totally harmless, but only that there is low toxicity under reasonable use, it does not mean you can eat it. No artists' pigments are made to 'food grade' or 'pharmaceutical grade' standards, so even if a certain coloring is considered non-toxic, it does not mean it's OK to ingest or carelessly handle. The designation here has been arrived at from, in most cases, the manufacturer's literature, art books and art reference works (see the bottom of the Pigment Database's main page for a complete list of reference works), MSDS sheets, the EPA manual: Environmental Health & Safety in the Arts: A Guide for K-12 Schools, Colleges and Artisans (full PDF here), The Art & Creative Materials Institute, Inc. (ACMI), The Health and the Arts Program - Great Lakes Centers at the University of Illinois at Chicago School of Public Health (UIC SPH), The American Institute for Conservation of Historic & Artistic Works has a collection of articles on art safety, The Consumer Product Safety Commission's Art and Craft Safety Guide (PDF, 250 KB) and Art Materials Business Guidance.

All paints and especially dry pigments can be hazardous if carelessly handled, but, if handled properly with common sense all but the most dangerous pigments can be used safely. Very few pigments used in the arts are edible, and even so called "Food Colors" are not meant to be used in large quantities and may have unknown side effects or allergic reactions.

WARNING: Always use a dust mask when working with any dry pigments. Work in a separate area of your studio away from children, pets or other living things. Do not smoke, eat or drink around any art materials. Dispose of all waste materials in an environmentally friendly and safe way.

A = Low hazard, but do not handle carelessly; Do not ingest; Avoid dust & spray.
B = Possible hazard if carelessly handled, ingested in large amounts or over long periods of time; Do not ingest; Avoid dust & spray.
C = Hazardous, use appropriate precautions for handling toxic substances, especially if working with the dry powder; Do not ingest; Avoid dust & spray.
D = Extremely Toxic, only attempt working with these pigments (especially the dry form) in laboratory like conditions with proper safety equipment (see "Prudent practices in the laboratory: handling and disposal of chemicals" at google books opens new window); or the PDF - Booklet Safe Handling of Colour Pigments Copyright © : BCMA, EPSOM, ETAD, VdMI - link from VdMI

The Side Notes Column:   Key Top ^ Page Top^

These are typically interesting things I have read, or information collected on a pigment that may be worth further study. Please remember that they are NOT statements of absolute fact. Many pigment qualities are rumors, old wife's tales and misconceptions repeated over and over until they accepted as fact without any scientific proof. I will include references (Ref) for further info.

Miscellaneous:

(hue) = When the word "hue" in in parenthesis (hue), it refers to a hue color not designated on the label, when the word "hue" is not in parenthesis is part of the pigment name as per ASTM guidelines.

(Ref) = A link to a reference source. This may be the reference source of the information that I have given, or just a link to more detailed information.

? = a question mark next to a name, note, or data code indicates that it may or may not be correct information due to conflicting information, questionable references, possible typo or other discrepancies in the manufacturer or other reference documentation. Further study is needed to clarify.

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