Pigments used in ink manufacture derived from inorganic mineral sources (in contrast to organic color pigments). There are several different varieties of inorganic pigments, classified primarily by their source.
The inorganic 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 single number. Thus, Cadmium Yellow below is listed in Part 1 as CI Pigment Yellow 37 and in Part 2 as No. 77199. These two sets of identifications accompany the individual entries on each separate pigment.
'Chromes'. Chromes are generally derived from various lead compounds, are fast-to-light (although some do darken on exposure to light, or on contact with sulfur gases), opaque and heavy. They hold up well when mixed with solvent- and oil-based vehicles, and are generally acid and alkali resistant. Chrome Yellows and Chrome Reds (comprising several shades ranging from greenish to orange) are produced from lead chromate mixed with other lead compounds, such as lead sulfate. Chrome Green is a mixture of Chrome Yellow and Iron Blue. Other chromes include Orange Chrome, Chrome Scarlet and Molybdate Orange, which are shades of Chrome Reds.
'Cadmiums'. Cadmiums are derived from various cadmium compounds, such as cadmium selenide or cadmium sulfide, are fast-to-light, and are highly resistant to alkalis and soaps, which makes them useful for printing soap packaging, or for long outdoor use. Cadmium-based pigments include Cadmium Red, Cadmium Yellow, and Cadmium Oranges, as well as Cadmium-Mercury Reds. The chrome and cadmium pigments are rarely used any longer, having been replaced by less potentially toxic organic pigments, except in cases where extreme chemical resistance is necessary.
'Irons'. Irons are derived from various iron oxides and include Iron Oxide Yellows and Iron Blues. Brown Iron Oxides can either be classified as red pigments or as brown pigments.
A lesser-used class of inorganic pigments include the Earth Colors, mined from sienna, umber, and ochre, are dull in color and are occasionally used in special applications. Ultramarine Blue and Ultramarine Violet possess high color purity and high resistance and lightfast qualities. Chromium Antimony Titanium Buff Rutile is used often as a brown pigment.
(See also Organic Color Pigments, and individual entries on the separate inorganic pigments.)