I have high school students creating a self portrait frieze in clay. They created plaster mask molds (now that was an intriguing thread for me) and pressed clay into the inside of the mask and then attached their clay faces to a clay slab. We took a walking tour to a garden statuary business where they did sketches and took pictures to base their final designs. They want to make their friezes look like old stone. I know shoe polish on top of the bisque is one way to go, but when I tested the shoe polish it turns blue. (I've never done this before!). I also have a Amaco Buf and Rub sample kit but the colors are too colorful. I'd like to give them choices to create an "old" ancient look perhaps with patina effects that I don't think the over or under glazes will create. Has anybody gone for this effect before, and do you have any suggestions?