Two cone 6 oatmeal-brown adjustable glaze recipes

Adjust matteness, working properties, crawling resistance

Left: G3933EF oatmeal based on Ravenscrag Slip.
Right: G3933 oatmeal based on a mix of G2934 matte and G2926B glossy base glazes.
Both have the same added colorants. The Ravenscrag version features several advantages. Most importantly, less tendency to crawl. It has better application properties, the slurry needs less water and it is naturally thixotropic. It has an extra option for adjusting slurry working properties: Changing the ratio of roast-to-raw Ravenscrag clay. It is responsive to cooling differences - more matte on slow cool versions of the C6DHSC schedule (e.g. 150F/hr), more glossy on faster cools (e.g. 250F/hr). And, its recipe is adjustable (e.g. raising the MgO if a more persistent matte is needed). And, the fired surface looks and feels better, interacting with dark bodies for richer color and varying in tone more for thinner and thicker sections.
This being said, the G3933 (right) is more easily adjustable for matteness (not requiring chemistry) and its materials may be easier for you to get. More iron oxide can also be added for extra color.

Related Pictures

The degree-of-matteness of this cone 6 glaze is adjustable

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This is G3933A oatmeal glaze fired at cone 6. But this is how it looks out of my kiln (using the C6DHSC drop-and-hold slow-cool firing schedule). On my clay body, Plainsman M390. At the thickness I have applied it. Using my materials and my method of mixing and application. Of course, having the recipe is the first step for you to make this (tap the code number above to see it). The next step is being able to adjust it. Adjust what? The degree of matteness. What I get here is a combination of the cooling rate (from the already-mentioned firing schedule), and the ratio of matte G2934 and glossy G2926B glazes I use (this is an 85:15 matte:glossy mix) to which I add the iron, tin and rutile. However, in your circumstances, the pure matte may be OK (if there is no cutlery marking). Or it might be too matte and require an increase in the percentage of glossy. Or, you might choose to cool the kiln faster or slow (to get more gloss or matteness).

Sometimes it is better to replace the base in a production glaze recipe

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Almost all ceramic glazes are a base recipe with additions of colors, opacifiers, variegators, etc. Our traditional G3933 oatmeal glaze is a good example (recipe on the left). It can produce rich brown silky matte surfaces, especially on dark burning bodies. But problems have emerged, especially a tendency to crawl. Much testing has yet to reveal the reason. Would it be possible to base the recipe on Ravenscrag Slip and achieve the same chemistry? Yes. And some unexpected benefits accrue. In the recipe on the right I sourced MgO (the key to the matte surface) from dolomite and Ferro Frit frit 3249 (earlier tests sourcing from talc were unsuccessful, off-gassing from the talc was puffing up the glaze with micro-bubbles). This G3933E recipe has the same chemistry (I derived it in my account at insight-live.com). It is not likely to be without problems, but it looks identical (with richer color from a little more iron oxide), it does not crawl and it's recipe and chemistry are flexible. It is glossy when cooled fast and silky matte when cooled slowly. The mix of calcine and raw Ravenscrag Slip also enable control over the slurry and application properties. I later tuned this recipe a little more and settled on G3933EF.

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Materials

Ravenscrag Slip
A light-colored silty clay that melts to a clear glaze at cone 10R, with a frit addition it creates a good base for a wide range of cone 6 glazes.

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