Ultramarine

Ultramarine is the blue of lapis lazuli. For most of its history it was made by crushing that stone, which came from a small number of workings in Badakhshan, in what is now Afghanistan, and it was the costliest pigment in the European painter's cupboard. Since 1828 it has been manufactured from cheap industrial minerals, and the synthetic material is chemically the same thing.^[1]

The colour additive listed for cosmetics in the United States is the calcined synthetic, defined by its process rather than by a mineral source.^[2] Natural ultramarine ground from lapis is not that listed material, and is not what a modern eyeshadow contains.

Ultramarine is a sodium aluminium sulfosilicate: a cage-like aluminosilicate framework with sulphur trapped inside it. The colour does not come from a metal ion, as it does in most inorganic pigments, but from the unpaired electron of a sulphur radical anion held in those cages.^[3] That is unusual, and it explains the pigment's one real vulnerability. It is unstable even in dilute acid, and decomposes to yield hydrogen sulphide, which destroys the colour.^[3]

The American colour additive listing defines the manufactured pigment by its process: pigments obtained by calcining at temperatures above 700 degrees Celsius a mixture of kaolin, sulphur, sodium carbonate, silicious matter, sodium sulfate and carbonaceous matter, but not necessarily all of these substances, to produce a single colour.^[4]

Lapis lazuli reached Europe by long trade routes and was priced accordingly, which is why replacing it was worth a public prize. In 1824 the Societe d'Encouragement pour l'Industrie Nationale offered 6,000 francs for a process that would make the pigment artificially and sell it below 300 francs a kilogramme.^[5]

Jean-Baptiste Guimet was awarded the prize in February 1828. The following month Christian Gmelin, at Tuebingen, contested it, claiming he had reached the result a year earlier and had chosen not to publish. Guimet replied that he had held his own formula back for two years. Mertens describes a third independent route as well, found by Koettig at the Meissen porcelain works, so the contest was not simply between two men; both of the priority claims are self-reported, and the secrecy that made the industry profitable is what leaves the question unresolved.^[5]

One claim should be set aside, and set aside carefully. That the ancient Egyptians wore powdered lapis as eyeshadow is repeated constantly and is not established. The 2022 study of kohl containers in the Petrie Museum found lead-based, manganese-based, silicon-based and carbon-based recipes, with copper minerals in two of the samples, and no lapis or lazurite among the minerals it reports.^[6] That study does not set out to test the claim, and absence in eleven vessels from a single collection is not evidence that the practice did not exist. The honest position is that the claim is unevidenced, not that it has been disproved.

Ultramarine is the practical route to a clean blue or violet in a powder product. Very few inorganic pigments give that hue at all, and the alternatives are organic lakes, which behave differently and carry restrictions of their own. The colour additive listing treats blue, green, pink, red and violet ultramarines as one family, describing them as complex sodium aluminum sulfosilicates whose proportions of each element vary with each colour.^[7]

It is opaque, stable to heat and light, and untroubled by alkali. Its incompatibility with acid is the constraint that matters in formulation, and it is why ultramarine is uncommon in products held at low pH.

The American listing, at 21 CFR 73.2725, permits ultramarines in externally applied cosmetics, including cosmetics intended for use in the area of the eye.^[8] That phrase is defined narrowly. Under 21 CFR 70.3, externally applied cosmetics are those applied only to external parts of the body and not to the lips or to any body surface covered by mucous membrane.^[9] A blue lipstick sold in the United States is therefore not coloured with ultramarine, though a blue eyeshadow may be.

The same listing sets purity limits of lead not more than 20 parts per million, arsenic not more than 3, and mercury not more than 1.^[8] In the European Union, ultramarines are a permitted colourant under Annex IV of Regulation (EC) No 1223/2009.^[10] The two regimes do not condition colourants in the same way, and a product lawful in one may not be lawful in the other.