List of inorganic pigments - Wikipedia
Inorganic Pigment Compounds - The Chemistry of Paint
. Iron represents an extraordinarily old, widespread and versatile family of relatively dull but extremely permanent and nontoxic pigments. All the common iron oxides have been used since antiquity (see under ) as the red, yellow and brown . Synthetic manufacture was known at least by the 15th century, though large scale production (and common use in artists' paints) did not emerge until the middle 19th century. The purest and finest oxides are produced from the precipitation and hydrolysis of iron salt solutions; hue and tinting strength are affected by hydration, particle size and by the presence of additives such as manganese. Because the manufacturing processes for iron oxide pigments can be exactly controlled, the modern synthesized versions usually are much purer, have smaller particle sizes and greater tinting strength, and are much more opaque than the natural iron oxides of the same type. They can also be mixed to match precisely any yellow, orange, red or brown hue, including near black browns. For these reasons the natural pigments have been almost entirely replaced by synthetic oxide mixtures, currently marketed in watercolors under the names venetian red, english red, indian red, or light red () and mars yellow (, ), but are now also used in hues formerly made of natural red () or yellow () iron oxides. Several transparent iron oxides with an extremely small particle size and a dark, relatively rich color are now also available, often used as wood or leather stains and occasionally as artists' pigments. These complexities make the earth colors a category that you must explore, trial and error across different brands of watercolors, to find the hue range and handling qualities you prefer.
Inorganic Pigments - Iron and chrome oxide pigments - …
A more exotic iron pigment is iron blue ( sometimes with sodium or potassium ions substituted for the ammonia ion) known to 18th and 19th century artists as Prussian blue, Berlin blue, Paris blue, Milori blue or Chinese blue (). This is the first modern synthetic inorganic pigment, discovered by chance in Berlin (hence the name "Prussian" or "Berlin" blue) in 1704 when the colormaker Heinrich Diesbach attempted to make a crimson pigment called Florentine lake from cochineal, alum, ferrous sulfate and some borrowed potash that was contaminated with animal blood. Diesbach communicated the recipe to his pupil de Pierre, who began to manufacture it in Paris. (Hence "Paris" blue. The label "Chinese" derives from the use of iron blue in the blue patterns on Meissen china, manufactured near Dresden.) Held secret for two decades, the manufacturing process was published in England by John Woodward in 1724, but by then alternative methods of production had been devised and the pigment was being manufactured throughout Europe and in America. It has been used in watercolors since around 1730 and is still sold today, although most watercolor artists now seem to prefer the more intense pigments. PB27 is a dark, unsaturated, staining, semitransparent and completely nontoxic middle blue; the color is sometimes adjusted by mixing with barium sulfate or alumina (which makes antwerp blue, a lighter, greener and less lightfast pigment). Iron blue is very reliable in pure form (both the ASTM reports and my own tests give it "excellent (I)" lightfastness), but it loses permanency if mixed with impurities such as potassium ferrocyanide or with other pigments such as titanium dioxide; my lightfastness tests demonstrated significant lightfastness variations across different watercolor paint manufacturers. Some descriptions of its quirks (for example, that it fades in masstone when exposed to strong light, but returns to its original color in darkness) have been uncritically handed down from the 19th century and are, as far as I can determine, myth. PB27 is currently manufactured as a precipitate from the reaction in solution of iron salts with sodium or potassium ferrocyanide, which is aged and oxidized to create the blue color. The pigment tends to agglomerate into rather stringy clumps that resist milling, but a special manufacturing method developed by BASF in 1982 (using the anodic oxidation of iron particles in hydrogen cyanide acid) produces very fine, pure and easily dispersable pigment particles with an atypically intense reddish color, valuable in printing inks. The pigment prussian green is a fused matrix of iron blue and lead chromate; cyanine blue is a mixture of iron blue and cobalt blue.