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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.

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Copyright 2006 Brad Walker.  All rights reserved.

Thanks to Lani McGregor of Bullseye for this tip.

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Copyright 2005-2006 by M. Bradley Walker.  All rights reserved.

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