If there is no lead or cadmium in your glaze (including no Frits which contain lead), and your kiln is not contaminated with lead, then you pass one toxicity test (for lead and cadmium). Can you use a certain glaze on a piece which will contain food and beverages? This is what most potters are interested in. And even clay particles with no toxicity get trapped inside lungs and thus are bad for potters to breathe. There are chemicals such as manganese which are known to be a health hazard when breathed in dry form, but are not believed to be a problem after being fired. Remember, all glazes in DRY form are unsafe for breathing, and you should use a good mask whenever dealing with dry glazes. You will see the AP Non-toxic label on the glaze bottle a circle with an AP inside. You don't want a lead-based glaze in the classroom for example. This is to reduce the risk of harm if a child drinks the glaze. In this sense, non-toxic only refers to lead and cadmium.Īll glazes sold in K-12 schools must be AP Non-toxic. All their glazes are either AP Non-toxic, which means non-toxic in liquid or dry form, or CL Cautions Required, which means it has proper labeling of ingredients for health and safety. TOXICITY IN PRE-FIRED FORM (LIQUID OR DRY)Ĭommercial glaze manufacturers label their glazes using ASTM D-4236. So reducing leaching as much as possible is always a good idea. Many of these materials are safe in low doses (for example, nickel, barium, selenium and cobalt), but toxic in high doses. There are other materials which may be toxic, but there is not enough evidence that they are unsafe at this time, so they are not regulated. Cadmium is used primarily to create bright orange and red colors. Lead is used to make glazes flow better at low temperatures. The two materials that are proven toxic are lead and cadmium. So we will attempt to clarify this without causing more confusion. It is a complex issue with many variables. Many people are confused about the safety of glazes, and rightfully so.
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