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Here is my setup to make brushing glazes and underglazes by-the-jar

To make a low SG version of G2934BL I have already weighed out a 340g batch (it contains 5g each of Veegum and CMC gum to gel the slurry and slow the drying). I use 440g of water initially (adjusting that according to experience in brushing behaviour). After shake-mixing all the powder in the plastic bag I pour it into the water on low speed and finish with 20 seconds on high speed. This produces a low specific gravity brushing glaze, it just fills this 500ml jar. In subsequent batches, I adjust the Veegum for more or less gel and the CMC for slower or faster drying. Later I also assess whether the CMC gum is being degraded by microbial attack - often evident if the slurry thins and loses its gel. Since each glaze recipe responds differently and changes differently over time, good notes are essential. We are working on dozens of these at any given time, each is code-numbered in our group account at Insight-live.com. This is so worthwhile doing that I make quality custom labels for each jar!

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Two low fire transparent highly fritted glaze recipes for pottery

These work well from cone 04 up, they are better than any commercial transparent brushing glaze we have used. And far better than glazes made using raw sources of boron (like ulexite, colemanite, Gerstley Borate). These glazes have lower thermal expansion and do not craze on any body we have tried (yet are ultra gloss and ultra-clear). They are G1916QL1 and G3879C. We developed them for use on the dolomite-based (rather than talc-based) L4410L low-temperature art clay body. These are a good demonstration of the technical and economic sense it makes to use highly fritted glazes at low temperatures. Having a good base glaze is the key to adopting low temperatures for your production. You would likely agree that no stoneware glaze has melting patterns like these shown in this melt fluidity test! These recipes and all details about their development and adjustment are openly available.

Medium fire white bodies used at cone 04. Is that smart?

Low-temperature white talc casting bodies have always been porous, 10-12% absorption is typical - pieces are basically just bisque-fired. People just pretend everything is fine! A stoneware potter might be horrified by this - until he/she sees the bright colors and brilliant glazes! If a dolomite body alternative is not available to you or your supplier is making a talc body that is no longer white there is an alternative: Use a middle-temperature white burning body. Why is this even possible? Their porosity at cone 05 is also 10-12% - but won't commercial glazes craze? Yes. So just make your own. This is G1916QL1 applied thickly on Polar Ice, P300, M370 (and L213 talc body), these are all plastic bodies but they can be adjusted for casting (removal of the bentonite). None crazed out of the kiln or after a BWIW test. I did this again with a thinner glaze application and at cone 03 (100°F hotter) and the results were even better. G1916QL1 can be mixed as a dipping or brushing glaze. But how can you guarantee no crazing? Fire even hotter, perhaps cone 02. Lower the thermal expansion further (as per instructions on its web page). And increase the silica in the body recipe at the expense of kaolin or ball clay (compensate with whatever bentonite is needed to get good casting properties). For a good cone 6 porcelain recipe for casting try L3778G. All of this can also be done with a plastic body, for that try L3778D.

Two methods to make your own low SG brushing glaze.

Dipping glaze applies and dries in seconds. Brushing glazes dry slowly and dry hard. Brushing glazes simply have gum in the recipe, dipping glazes typically do not. This is the Alberta Slip cone 6 base, made jet black with 4% black ceramic stain (our code G3914A). We normally mix this as a dipping glaze but I have made a 500ml jar of low SG brushing version using both of the following methods. These methods will work for almost any glaze recipe (for those having exceptionally high clay content less Veegum is needed). 1) Shake together, in a plastic bag, 340g of mixed glaze powder with 5g of Veegum and 5g of CMC gum. Add that to 440g of water in a kitchen blender and mix on high speed until it gels (the gums resist mixing so the highest speed for at least 30 seconds is needed to prevent lumps). 2) Take 680g of dipping glaze (assuming it is about 50:50 water:powder you get 340g of dry), put that in the blender with another 80g of water and proceed as in method 1. Less total water is being used because the dipping glaze might not be exactly 50:50 water:powder. During mixing, if it gels too much add the extra 20g of water.

Amaco PC-20 vs Ravenscrag Floating blue

G2917, which I mixed as a brushing glaze, is on the right. This is not sold in jars, I make my own labels as part of the demonstration that it is possible to make your own brushing glazes (ink-jetted onto regular paper, cut 62mm wide (2 7/16") and held securely on with 2 7/8" transparent packing tape). This glaze is less runny but lacks some of the floating white colouration. But that can be achieved using Alberta Slip floating blue L4655, it employs titanium instead of rutile (and relies on the rutile/iron mechanism for the blue color).

Learn to mix any of your glazes for these three application methods

Potters are used to making dipping glazes that they weigh out and mix from recipes. Hobbyists commonly use bottled commercial brushing glazes. Did you know that a dipping glaze can be turned into a brushing glaze by the addition of Veegum (or Veegum CER) and water? Do you know what a base-coat dipping glaze is? Here is a quick overview: Dipping glazes need to go on to bisque ware evenly, be thixotropic enough to hold on at thickness and drain and dry quickly. But they don't need to dry hard. Brushing glazes need a cohesive slurry that dries slowly and hardens well on drying. They also must adhere to the body really well so that multiple layers can be applied (individual layers go on thin). Base-coat dipping glazes are in between, they need to dry fast enough and gel well enough to make application by dipping possible (although less practical) and they need to adhere well enough to tolerate another layer without letter go of the body.

Control gel using Veegum, brushing properties with CMC gum

This is G1214Z1 brushing glaze (with 5% titanium added). For a 340g powder batch (to get a pint) my initial target is 5g CMC gum and 5g Veegum. CMC controls drying speed and Veegum the amount of gelling. I first mix the CMC with the powder and shake the whole batch in a plastic bag. Then I add it all to 440g of water in the blender jar and mix it well (making sure no agglomerates remain (stage 1). Stage 2 is adding the VeeGum slowly, while high-speed blender-mixing, this is important because it enables tuning the degree of gel (which cannot be predicted). Because this recipe has little clay, it took all 5g of Veegum without overgelling (the entire mass moved freely in the mixer jar). But it did gel overnight (so 4g would be better next time). By contrast, it is the brushing behavior that demonstrates whether the amount of CMC is right. Not enough and coats dry too fast and go on too thick. Too much and it dries too slowly and too many coats are needed.

Here’s how we make a base brushing engobe

This brushing engobe is thick and gooey (because it contains CMC gum), so it is practically impossible to sieve. Our regular propeller mixer is not able to break up the tiny agglomerates of New Zealand kaolin. But 30 seconds of blender mixing makes it as smooth as silk. To make this liter of brushing engobe we use 800g of powder and 10g of CMC gum in 800g of water. Because of the very high clay content this does not require Veegum to gel it. The CMC gum greatly improves the brushing properties. It also thins the slurry enough to enable its lower-than-normal water content, making it more suitable for painting onto leather-hard ware, minimizing the number of coats needed.

A 2oz jar of underglaze dries down to 21g of powder. That is bad and good!

Only a part of that 21 grams is actual stain powder, it is mixed into a medium. A 16oz jar of another color yielded 190g, a slightly better percentage of powder-to-water. The high water content is actually a benefit, they condition it with a clay that causes it to be thixotropic (gels). In one scenario we calculated a 1500% saving in making your own underglaze vs. buying these jars, that is a more feasible idea than you might think. With out setup we can weigh and make a 1 pint jar of brushing glaze/underglaze in ten minutes.

Make and sell your own jars of glaze at your teaching studio

Your studio or workshop can save a lot of money making and even selling your own glazes to students (at least for common colors and types). The supplies shown here enable printing quality labels on ordinary paper and applying them to jars that cost about $2. What about the glazes themselves? Just do what glaze companies do: Add stains to a base transparent glossy or matte glaze (for example G1916Q for cone 04 or G2926B for cone 6). Each 16oz jar needs 350g powder, 450g water, 5g CMC gum and 5g Veegum (leave out the Veegum and use less water for thicker coats). Stains are expensive (5-20 cents/gm here in 2024), at 7.5% (25g) that is $1-5 per jar. The materials for the G1916Q base cost $10/kg, and for G2926B $4/kg. Thus each jar costs $3.33 and $1.33 respectively. Making recipes of 5000g at a time would enable making 15 jars. A best-case is thus about $5/jar, worst case about $10/jar (compare that with commercials that are about $15-70). Of course, you can save money by looking for deals on materials and stains and recycling jars. Consider other advantages of making your own: You can tune the rheology, you know what is in it, you can adjust recipes to fit your clay bodies (to prevent crazing or shivering).

Are you worried about labelled, testing and SDSs? Take a look at ASTM D-4236 and see if you still need to worry.

Blending an engobe and a glaze to produce an underglaze

These fired samples demostrarte how you could develop your own Stroke & Coat glazes. I made these blends by dewatering an engobe (L3954B) and glaze (G2926B) and then hand-mixing line blending them. The left column is the fired blends (cone 6), the right one the unfired ones (showing the increase in soluble salts as the percentage of glaze increases). The right one shows the increase in melt fluidity. The top ones are 30:70 glaze:engobe and the bottom ones are 90:10 glaze:engobe. Notice the big change in melt fluidity between 60 and 70% glaze (third and fourth from bottom). And that the 70% one is quite glossy even though it has very low melt fluidity. Somewhere between 60 and 70 we could isolate a glaze-like product having underglaze stability. Stains could be incorporated and the proportion of glaze:underglaze adjusted according to its effect on melt fluidity. Doing this yourself enables targeting an exact melt fluidity for each color at the target temperature. The commercial product does not do that. You can also use more stain then they do to get more vibrant color for thinner applications.

Brushing glazes on large pottery items is surprisingly practical

I applied this cone 10R 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 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).

Glazing large bowls inside-and-out using brushing glaze

This wheel-thrown bowl is large, heavy and thick walled. There are pouring techniques to apply different colored dipping glazes to the inside and out but they are cumbersome and slow. It turns out that the hobbyist way of glazing is actually better - by brushing. I make these 500ml jars of brushing glaze and tune the percentage of gums to get the painting consistency and drying time best for me. Applying multiple coats by brush took only a few minutes and no wax resist or any other tools were needed. And it was easy to meet the two glazes in a straight line at the rim using the brush. The inside glaze is G2936B and outside is G2926B.

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