|Monthly Tech-Tip |
The glaze on the left is 85% of a calcine:raw Alberta Slip mix (40:60). It was on too thick so it cracked on drying (even if not too thick, if others are layered over it everything will flake off). The center piece has the same recipe but uses 85% pure raw Alberta Slip, yet it sports no cracks. It should be cracked much worse than #1. How is this possible? 1% added CMC Gum (via a gum solution) was added! This is magic, but there is more. It is double-layered! Plus very thick strokes of a commercial brushing glaze have been applied over that. Yet no cracks. CMC is the secret of dipping-glazes for multi-layering. The downside: More patience during dipping, they drip a lot and take much longer to dry.
In traditional ceramics and pottery dipping glazes can be of two main types: For single layer and for application of other layers overtop. Understanding the difference is important.
CMC gum is indispensable for many types of ceramic glazes. It is a glue and is mainly used to slow drying and improve adhesion and dry hardness.
Albany Slip successor - a plastic clay that melts to dark brown glossy at cone 10R, with a frit addition it can also host a wide range of glazes at cone 6.
Ask yourself the right questions to figure out the real cause of a glaze crawling issue. Deal with the problem, not the symptoms.