Glossary

The acid resistance is an important feature of glazes that are to be used for dining and drinking dishes. Food contains acidic substances that can visually impact the fired glaze after use over a long or longer period, so that, from the user's point of view, the finished ceramic can get a defective surface due to acid wear!

 

Most of the plain acid resistance does not take into account a possible health risk from escaping substances. For this purpose, the finished product must be tested for the possible migration of lead and cadmium in accordance with the current legislation for Consumer Goods Ordinance (according to EC 1935/2004 with test guidelines 84/500 / EEC including 2005/31 / EEC). An enhancement of this standard with regard to the solubility of cobalt and titanium dioxide is being planned, but has not yet been implemented in valid law !

 

Although these solubility values ​​primarily have nothing to do with acid resistance, we have nevertheless decided to inform you about the use of cadmium and lead compounds in our glaze formulations (even if these are present in the glaze powder as a compound that does not require labelling) ! As soon as either the recipe contains one of these components and you bring the finished ceramic onto the market, you must have the pieces that were created under your production conditions examined in an accredited laboratory for the possible migration of lead and cadmium. This is also necessary if you cannot completely rule out that lead and cadmium compounds have entered your ceramic in other ways (e.g. through vapours in the kiln lining).

 

As soon as we indicate the acid resistance with "Yes" or "No", there are no cadmium or lead compounds in the formulation.

 

Test condition: Treatment of a glaze sample for 20 hours with vinegar essence (25% acetic acid). Due to the increased concentration of the acid in contrast to "food-typical" concentrations, the long-term wear is to be simulated!

 

Assessment: Optical wear.

If the acid resistance is given as "Yes", then no visual attack can be seen. However, the acid resistance depends on the type of acid used. If so, with other acids e.g. diluted hydrochloric acid or butyric acid a different result can be achieved !

If, on the other hand, the acid resistance is given as "No", then the impact on the glaze surface ranges from "slightly rougher" (if you touch the glaze with your fingernail) to a complete "etch" of the glaze, so that the blank body appears. In order to prevent customer complaints, the use of these glazes for dishes is not recommended !

In the case of lead and cadmium compounds that are label-free, on the other hand, the plain acid resistance was not determined for the above reasons.