Encapsulated stains can reach their limits in a glaze host at cone six and begin to dissolve and decompose. That is an obvious problem on a food surface. But in a less fluid underglaze they can survive longer. The bright orange color on the left was likely done this way. The transparent over glaze is isolating it from any contact with food or drink. However people are more wary of the risk of glazes leaching heavy metals and having bright colours on food surfaces may not send the right message.
This is a type of stain manufacture that enables the use of metal oxides (like cadmium) under temperature conditions in which they would normally fail.
Ceramic glazes can leach heavy metals into food and drink. This subject is not complex, there are many things anyone can do to deal with this issue
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