Testing an Overglaze for Lead Content
Overglazes are solutions which are applied
to the surface of the glass prior to firing. Products range from
"devit sprays," which are used to prevent
devitrification, to various fluxes
and related solutions used when working with glass. Many of
these products contain lead and are not safe for food-bearing
surfaces, while others are food-safe.
One fairly simple way to determine the lead
content of an overglaze is to spray the product onto a glass that
contains sulfur and then fire to full fuse. Sulfur-containing
glasses will react with lead (this is called a lead-sulfide
reaction) and darken after firing. The more lead in the glaze,
the darker the surface reaction.
One good glass to use for this test is
Bullseye's French Vanilla opal (0137). Spectrum's System 96
line contains a similar glass (Almond Opal). Although this
test is not perfect, it will give you a good idea of the relative
lead content of two different overglazes.
Copyright 2006 Brad Walker.
All rights reserved.
Thanks to Lani McGregor of
Bullseye for this tip.