Abstract: Glass frits are disclosed which are essentially free of lead and contain 0.05 to 15 mol-% sulfur and/or sulfides, preferably zinc sulfide. A process is disclosed for producing a glass frit by melting a mixture of oxides and/or non-oxide compounds (fluorides, carbonates) at temperatures of 1,000.degree. to 1,300.degree. C., followed by sudden cooling, characterized in that the glass frit contains between 0.05 and 15 mol-% sulfur, zinc sulfide or other sulfides. The glass frits can be used in enamel barrier layers for stopping the migration of silver.

Abstract: A process to synthetize zircon as an ultra thin coating and comprising: (A) mixing an alcoholic sol resulting from hydrolysis of a silicon alkoxide with an alcoholic solution of a chelated zirconium compound and in the presence of and with a doping agent, until a homogenous mixed sol is obtained; (B) forming a matured sol containing colloidal particles and/or the polymeric entities from the mixed sol; (C) forming a coating of the matured sol on a microporous substrate; (D) drying slowly the sol coating into a gel coating free of flaws; and (E) firing the gel coating at a temperature of 900.degree. to 1500.degree. C. to form an ultra thin zircon layer. Use of the zircon layer obtained above as an ultrafiltration membrane or as a protective coating.