A potter uses a 70% potash feldspar, 20% whiting, 10% kaolin glaze for a crackle cover over iron oxide brush strokes. While it fires crystal clear, it has a problem: it crawls. While it can be flocculated with Epsom salts, and the application and dry adherence are fairly good; this crawling problem is occurring. By mixing it as a DIY brushing glaze we can fix three of its problems without changing the recipe: Its tendency to go on too thick, the entrained bubbles in the clear glass and the crawling. Don’t dismiss this idea immediately. This is a special-purpose surface and brushing can be done more quickly than you might think. Careful control of thickness is possible and the CMC gum in the glaze will make it adhere much better (eliminating the crawling). The consistently thinner coverage will also make it possible to produce crystal clarity with fewer micro-bubbles in the glass. A hybrid approach is also possible: Pour glazing the inside and brushing the outside.

This picture has its own page with more detail, click here to see it.
This is a slurry of pure feldspar. A tiny addition of powdered Epsom salts flocculates it enough that it can remain suspended for days; without that, the watery slurry settles very quickly. Remarkably, it can even be applied to absorbent bisque despite containing no clay. But suspension is only one requirement of a usable glaze slurry. The deposited feldspar layer is extremely permeable, so the bisque sucks water through it almost unhindered. The coating therefore builds at remarkable speed—the piece must essentially be dipped in and out with no dwell time. Then a second problem appears. While the coating is damp, it can be handled, but after drying it has almost no strength: The feldspar particles form a fragile, easily disturbed powder layer. The Epsom salts have solved suspension, but not binding.
Some industrial dipping glazes likewise contain little or no clay. They compensate using organic binders and rheology modifiers such as CMC gum. These retain water, control application behavior and, especially important here, bind the particles together after drying so the glazed ware can survive handling before firing.

This picture has its own page with more detail, click here to see it.
The outsides of these reduction-fired bean-pots are a unique challenge to glaze evenly and drip-free using dipping or pouring (also, a much thinner layer is needed inside the flange). A gummed brushing glaze is a solution. But how can one convert a cup of dipping glaze into a brushing glaze? CMC gum powder - it slows down drying and imparts brushing properties. Since our dipping glazes are about 50:50 water:powder, I blender-mixed 3.75g CMC gum powder into 1000g of slurry to get ~0.75% concentration (depending on your mixer it might require more). Triple-layer brush-glazing this piece takes about five minutes. I use two brush types (fan and hake) and different techniques for each zone. It dries really hard. If the gum over-thins your glaze, a water-reduced version is needed. Assuming it has settled somewhat pour off or sponge off some of the water and add the CMC gum to that. Don’t forget, it has to be blender mixed.
| Glossary |
Brushing Glaze
Hobbyists and increasing numbers of potters use commercial paint-on glazes. It's convenient, there are lots of visual effects. There are also issues compared to dipping glazes. You can also make your own. |
![]() PayPal | No tracking, No ads, No paywall, No transient content! Just organized, concise information constantly updated and improved. Was this helpful? Consider supporting me. |
Buy me a coffee and we can talk