Researchers have discovered a new cobalt-doped barium aluminosilicate colourant that withstands the high temperatures found in a kiln and provides a bright colour to glazed tiles.
In a paper published in the journal ACS Applied Optical Materials, the scientists point out that many brilliant blue pigments—like those in antique Chinese porcelain or works by Claude Monet—make use of cobalt-based compounds, including the famous “cobalt blue.” In mineral form, the metal has high chemical and thermal stability, and those properties make cobalt aluminate one of the only pigments suitable for high-temperature applications, including pottery glazes.
Today, cobalt is used in lithium-ion batteries, and demand for the metal ore will likely increase as the need for battery power grows. As a result, scientists, including Peng Jiang and colleagues, are searching for alternative pigments that require fewer cobalt ions and still maintain a bright blue hue.
The team based their new pigment on a barium feldspar mineral (BaAl2Si2O8), which also features high temperature and chemical stability. Compounds containing barium, aluminum, silicon and cobalt were ground together, pressed into a sheet, then heated to above 2550 degrees Fahrenheit to form the pigment.
Then, the researchers mixed the powder into a ceramic glaze, sprayed it onto tiles, and fired them to produce glazed pieces of pottery. The pigment was stable at temperatures up to 3200 degrees—well above the typical firing temperature of a pottery kiln—and only experienced slight colour changes when exposed to either acidic or alkaline solutions, demonstrating the compound’s stability.
Tiles sprayed with the pigmented glaze maintained a smooth, bright surface that deepened in colour as the cobalt concentration in the pigment increased.
The researchers say this new powder substantially reduces the amount of cobalt needed, resulting in a cheaper, easier-to-produce blue ceramic pigment.
