Color Breaks Free of Heavy Metal

Chemists have found a safe substitute for the brilliant yellow and red cadmium-based pigments used to tint glass and ceramic glazes. The new pigments contain no heavy metals, but are vivid and durable, scientists report in the 27 April issue of Nature. The pigments should be commercially available within a year.

Cadmium pigments are almost completely insoluble, so you won't get cadmium poisoning from drinking coffee out of a glazed mug. But if the mug breaks and you throw it away, the intense heat of the neighborhood incineration plant can free the cadmium, a poisonous metal, and potentially release it into the environment. Most governments strictly regulate the handling of cadmium pigments, but they are still used to tint glasses, glazes, and ceramics because there has been no safer alternative.

To create a substitute, chemists Martin Jansen and H. P. Letschert of the Max Planck Institute in Stuttgart, Germany, mixed solid calcium and lanthanum in a hot stream of gaseous ammonia--a mix they knew would create bright colors. They systematically varied the relative proportion of calcium and lanthanum in the mixture. This tuned the oxygen-to-nitrogen ratio in the resulting solid to anywhere between 0.5 and 2, creating colors ranging from bright yellow to deep red. The palette precisely matches the colors of the cadmium-based pigments. Although these nontoxic pigments are 20 times more expensive than the old ones, Jansen is confident that consumers will want an environmentally friendly glaze. He estimates that the premium pigment would only add about 10 cents to the price of a dish.

Frank Di Salvo, a solid state chemist at Cornell University in Ithaca, New York, thinks the new tint will start a wave of innovations in nontoxic inorganic pigments. "This is a great first start," says Di Salvo, "You could eat the stuff and it wouldn't hurt you."