I am in the process of starting up a small business. I make aquarium ornaments and other decorative pieces out of earthenware. I want to add some color to my work without glaze. I'm considering using two or more types of clay in a single piece. How do i know if two clays can be blended into a single piece? I know it has something to do with the shrinkage rates and grog %. But where do I get this information and exactly how close do two types of clay have to be to be workable together. Also how do I know if a particular clay is aquarium safe. The supplier came right out and told me the first type of clay I used was safe but they aren't being nearly as helpful now for some reason. How do I know if the clay will hold up in water? How do I know if it will affect water chemistry?
I do not have a kiln. I currently drive 2 freakin hours round trip to get my work fired. This makes glazing pieces extremely costly because of gas and additional kiln costs. But this is not the real reason I don't glaze. I like the look unglazed pieces take on once they mature. geocities.com/landonwebb
there are a few mature pieces on my website. Take a look and you'll see what I mean. I want to blend clays so that i can maintain that effect. Glaze would add color but it would be so smooth that the algae would not colonize the piece nearly as well and it would not look as attractive.

Freshwater Fish Species