The colorful glaze on that ceramic mug of yours may look nice, but there's a chance that it could contain toxic substances. US scientists have thus created a safer type of glaze, that incorporates tiny particles of silver and gold.
Although some manufacturers have switched to less harmful compounds, ceramic glazes traditionally utilized heavy metals such as barium and cadmium – and some glazes still do. When used in the quantities required to produce particularly bright colors, these metals can leach out of the ceramic item over time, potentially causing health problems.
Led by Dr. Ryan Coppage, scientists at Virginia's University of Richmond therefore experimented with adding less-toxic silver and gold nanoparticles to a clear glaze base. Reducing the metal particles to such a small size (between 1 and 100 nanometers each) altered their optical qualities, as did the kiln-firing process.
In the finished ceramic test samples, the silver particles produced red or bright green colors, while the gold particles showed up as deep reds and blues. Different colors can be produced by using different concentrations of the nanoparticles, or by combining the two types of particles in various ratios.
And yes, silver and gold themselves are heavy metals. That said, in the amounts needed to produce the desired colors – about 0.01 percent of the glaze by weight – they reportedly shouldn't pose any risks. By contrast, other heavy metals used in glazes make up 5 to 15 percent of the weight, or even 50 percent in the case of manganese.
Additionally, because such small amounts are required, silver- and gold-based glazes shouldn't be very expensive. It is estimated that the amount of glaze required to cover a single ceramic cup would cost about 30 to 40 cents.
The research is described in a paper that was recently published on the American Chemical Society's SciMeetings online platform.
Source: American Chemical Society
