Sometimes it happens that I want to alter a glaze after it has been made up and the water added.  Say, for instance, I have a bucket of glaze that I know is 15% silica and I want to experiment with it by adding another 5% silica to make it 20%.  At the dry stage this is no problem, but now that it has the water in it I have to figure out how much of it's weight is water versus the formerly dry material.    I'm thinking:  Measure the specific gravity of the mixture.  Lets assume it is 1