Method for reducing acid lead solubility of a lead-containing glaze or frit

Claim 3

A method as claimed in claim 1 wherein the lead silicate contains from 1/2 to 5 percent of alumina in addition to lead and silica.

Claim 4

A method as claimed in claim 2 wherein the glass contains about 65 percent of lead oxide and about 35 percent of silica.

Claim 5

A method as claimed in claim 1 wherein a substantially lead-free frit that has previously been ground to the degree of fineness desired in the slip is mixed with the leached glass particles, and the slip is formed by suspending the resulting mixture.

Claim 6

A method as claimed in claim 1 wherein glass particles finer than about 5 microns are separated from the ground glass prior to the formation of the slip, and the slip is formed from the remaining coarser particles.

Claim 7

In a method for reducing the acid lead solubility of a lead-containing glaze, enamel or the like slip, which method comprises grinding a glass consisting essentially of not more than 70 percent of lead oxide calculated as PbO and at least 30 percent of silica to substantially the degree of fineness desired in the slip, and forming a slip by suspending the glass particles in water, the improvement of leaching the ground glass in a dilute aqueous acid, controlling the temperature and the duration of the leaching step to reduce the soluble lead content at the surfaces of the glass particles to not more than about 0.8 percent, based on the weight of lead, calculated as PbO, removed from a 0.5 gram sample of the finely divided particles upon exposure to 500 ml. 0.25 percent hydrochloric acid at 20*C for two hours, and washing the leached glass particles before the slip is formed.

Claim 8

In a method for reducing the acid lead solubility of a lead-containing glaze, enamel or the like slip, which method comprises grinding a glass consisting essentially of not more than 70 percent of lead oxide calculated as PbO and at least 30 percent of silica to substantially the degree of fineness desired in the slip, and forming a slip by suspending the glass particles in water, the improvement of leaching the ground glass in a dilute aqueous acid, controlling the temperature and the duration of the leaching step to reduce the soluble lead content at the surfaces of the glass particles to not more than about 0.8 percent, based on the weight of lead, calculated as PbO, removed from a 0.5 gram sample of the finely divided particles upon exposure to 500 ml. 0.25 percent hydrochloric acid at 20*C for two hours, and washing the leached glass particles before the slip is formed.