|Monthly Tech-Tip |
These brush-strokes of gummed glaze are painted onto an already-fired glaze (the gum enables adherence and drying without cracking). Notice brush strokes hold their character. The brown glaze on the left has 1.6 specific gravity (SG) and about 1.5% CMC gum. The white one has the same gum content but an SG of 1.5. It's brush stroke has flattened and it is running downward. This is not happening because of the lower SG, commercial glazes with an SG down to 1.3 can perform well. How? Because they also have Veegum to thicken them. That reveals thus secret: Gum needs particle surface area to work its magic. We can get that with a bentonite addition (it is fine particled like Veegum). The dried strokes on the right were much better, that glaze adds 2% bentonite. That made all the difference, it painted beautifully.
Hobbyists and increasing numbers of potters use commercial paint-on glazes. It's convenient, there are lots of visual effects. There are issues compared to dipping glaze. You can make your own.