Pigments used in the manufacture of printing inks derived from derivatives of coal tar (organic pigments are frequently referred to as "Coal Tar Colors"), in contrast to inorganic color pigments which are derived from mineral sources. The inorganic pigments are classified according to chemical makeup (chromes, cadmiums, etc.), while the organic pigments are classified by color. The organic pigments listed below are classified and identified in the Society of Dyers and Colorists' Color Index. Each classification consists of two parts, corresponding to the two parts of the Index: The first part identifies each pigment with a CI number, which accompanies a description, usage, and technical information. The second part lists each pigment by chemical composition, and assigns each one a number. Thus, Para Red below is listed in Part 1 as CI Pigment Red 1 and in Part 2 as No. 12070. These two sets of identifications accompany the individual entries on each separate pigment.
There are literally thousands of organic pigments, many of which are no longer in use, or which are used very seldomly. The pigments listed below are among the most commonly used in the industry, as of this writing.
'Yellows'. Yellows comprise the Yellow Lakes, which are transparent pigments used as a yellow to cover other inks but not hide them, Tartrazine Yellow Lake (also called FD&C Yellow No. 5 and used as a dyestuff in foods), Hansa Yellows, and Diarylide Yellows, which are the most common yellow pigments used in printing inks. Fluorescent Yellow is also used in some specialty applications. Organic Yellows are commonly used to replace Chrome Yellows.
'Oranges'. The most common orange pigment is Diarylide Orange, a transparent yet not very fast-to-light pigment. Other assorted orange materials tend to be used where orange pigments are necessary, and include DNA Orange, Pyrazolone Orange, Fast Orange F2G, Benzimidazolone Orange HL, and Ethyl Lake Red C.
'Reds'. Reds include Para Reds, Toluidine Red, ["Permanent Red "R""], Carmine F.B., Naphthol Reds and Rubines, Permanent Red FRC, Bordeaux FRR, Rubine Reds, Lithol Reds, BON Red, Lithol Rubine 4B, BON Maroon, Rhodamine 6G, Lake Red C, BON Arylamide Red, Quinacrinone Magentas, Copper Ferrocyanide Pink, Benzimidazolone Carmines and Reds, Azo Magenta G, Anthraquinone Scarlet, and Madder Lakes.
'Blues'. Blues include Phthalocyanine Blues (the most commonly used group of organic blue pigments), PMTA Victoria Blue, Victoria Blue CFA, Ultramarine Blue, Indanthrene Blue, Alkali Blues, and Peacock Blue.
'Violets'. Violets overlap slightly with some of the bluer reds (such as Benzimidazolone Bordeaux HF 3R (see Benzimidazolone Carmines and Reds), and also include such pigments as PMTA Rhodamine, PMTA Violet (also known as Methyl Violet), Dioxazine Violet (RL) Carbazole Violet, Crystal Violet, Dioxazine Violet B, and Thioindigoid Red.
Also available in the organic class of color pigments are the Fluorescent Pigment Colors, which are used primarily in screen printing. They lack the lightfastness, variety, and mixability of the regular pigments, and are more expensive and require application of thick films or multiple passes to achieve the desired effectiveness. (See Fluorescent Pigment Colors.)
See individual entries on separate pigments.
Organic color pigments, unlike the (usually) straightforward inorganic color pigments, are chemically described by complex ring structures which, for the sake of clarity, have been omitted from the individual entries. Detailed molecular structures for each of these pigments can be found in The Printing Ink Manual or in the Color Index published by the Society of Dyers and Colorists (see bibliography).