I am working with a ceramicist doing prototyping work for a new product. I would sincerely appreciate any input/advice on these points:

1. Needing to achieve a gray and a sandstone color to the clay body, which is an earthenware. I know this can be done with mason stains, however, my ceramicist is very adverse to working with these stains claiming they have toxic elements. Is this correct? Aren't they trace amounts?

2. Is there another way to achieve these colors in earthenware?