UNTIL recently, the glaze on most Mexican pottery contained lead. This was practical: lead fuses into a shiny glaze at less than 800° Celsius, the most that artisan kilns achieve, whereas the alternatives required more than twice the heat. But it was a problem for Mexican potters, of whom the government reckons there are between 2m and 4m. They suffered from lead poisoning, and to a lesser degree so did customers who bought their plates and cups. Their products were banned from the American market, where their hand-painted beauty could fetch much higher prices than in rural Mexico, where the pots were merely a practicality.