Abstract: Crystal articles are treated at high temperature by a gas produced by the vaporization of sulfate(s) of ammonium and of aluminum or of iron. For example, a temperature of 480.degree. C. is maintained for 15 minutes to 3 hours. After the article has cooled, the initial purity of the treated surface can be restored simply by washing the treated surface with water or soapy water. The process is carried into practice by placing the treatment powder 4 at the bottom of the article 1 to be treated and closing the opening 2 of the article 1 by means of a graphite plate 5. A device 8 holds the plate 5 in the opening 2. The invention provides a means of limiting the migration of heavy metals, such as lead, for articles made from crystal.