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URL: Youtube Video: Brush Glazing Large Pieces
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By blender-mixing 10 grams of CMC gum into a liter of my standard dipping glaze I can apply it to the insides and outsides of large bowls quickly and evenly. This is better than any other method I have used.
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Brushing glazes on large pottery items is surprisingly practical
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I applied this transparent inside and out on both bisque and bone-dry ware using only a small brush (of course, a larger one or a fan brush would be better). I have done up to 35 lb bowls this way. This is not a commercial brushing glaze, it is a dipping glaze that we mix ourselves: G1947U. We add 10g CMC gum powder to one liter of a water-reduced version of the slurry. Blender mixing makes it possible to mix in the powdered 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).
It might surprise you that handmade tile is often glazed using brushing. For example, the glaze can be squirted onto a file and spread with a large brush in seconds. This can be done on a passing conveyor or in batches on a table.
Add CMC gum to a dipping glaze slurry for brushing
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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.
Fan Brushes - The best way to apply brushing glazes
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These seem to work well for brushing glazes whether the bristles are fine or coarse, stiff or soft. The key to their utility is the shape. An ordinary brush, when dipped into glaze, pulls together - minimizing the total load it can hold and the breadth of stroke it can make. But these stay fanned. Each bristle has access to more glaze and thus the brush can deliver more. The fan shape also assists in spreading the glaze evenly over the surface, after all, that is the purpose, spreading evenly not decorating. A fan brush can be dipped and brushed in rapid succession, delivering a lot of glaze to the surface. And, these brushes are much easier to clean. Of course, these only work if the glaze contains enough gum to retard its drying and gel enough to stay in place. These were purchased at Michaels, they are high quality and inexpensive.
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