We normally make a low specific gravity pint of slow-drying brushing glaze using 340:440:5:5 powder:water:Veegum:CMC proportions (this is ~1.5% of each of the gums). But where thick coverage of large areas is needed a potter can quickly convert a dipping glaze for painting. How? By blender mixing some CMC gum into it (with no Veegum the specific gravity is high enabling thicker layers). Since we mix most of our dipping glazes to about 50:50 water:powder then 340g powder is yielded by ~680g slurry. I can thus blender mix 5g CMC gum into 680g of slurry to quickly make a pint. Why no Veegum? Faster drying, and as noted, thicker coverage (still much slower drying than dipping consistency). This piece is difficult to cover using dipping or pouring (without having a large bucket of slurry). In addition, I need a thin glaze layer inside the flange and quite thick elsewhere. These issues were easy to accommodate by brushing on three coats. In fact, I can quickly glaze large 15 and 35 lb bowls, while rotating on the wheel, inside and out, using this same technique.
I applied this cone 10R transparent inside and out on both bisque and bone-dry ware using only a small brush. This is not a commercial brushing glaze, that would be super expensive for large pieces (I have done up to 35 lb bowls this way). This is a dipping glaze that we mix ourselves: G1947U. We add 10g CMC gum to one liter of a water-reduced version of the slurry. Blender mixing makes it possible to mix in the gum and tune water content for the best brushing experience. The gum slows down the drying speed dramatically so there is plenty of time to brush it into place (while the wheel is turning). The gum also greatly increases the cohesion, enabling pouring it without drips, even in a long thin stream. Many pieces were done like this in recent kiln loads (including application onto a leather-hard 40-inch tall vase), the evenness of coverage was the best I have ever gotten (of any technique).
The cone 6 mug on the left has the G3933A glaze, applied as a dipping glaze. It turned out poorly - crawling from corners and looking thin and washed out. I made a brushing glaze version of this (which adds 1.5% CMC gum), I keep it around for this very purpose. It has a high specific gravity (unlike commercial ones that have high water contents - they will run and go on too thin if you try this). Because of the gum it dries hard, there is no shrinkage or cracking. On a second firing, using the C6DHSC schedule again, (mug on the right) the surface is transformed - thicker, more vibrant color (being picked up from the underlying body).
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.