G2928C - Ravenscrag Silky Matte for Cone 6

Modified: 2022-01-30 15:59:15

Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com.

Material	Amount	Percent
Ferro Frit 3134	11.00	10.4
Talc	8.00	7.6
Ravenscrag Slip	60.00	56.9
Nepheline Syenite	13.00	12.3
Wollastonite	1.50	1.4
Calcined Kaolin	12.00	11.4
Added
Tin Oxide	5.00	4.74
110.50		100

Notes

This works well on Plainsman M340, but especially on a whiteware like M370. Produces an ivory white with some fleck. The surface is very silky, reminiscent of a cone 10 dolomite matte. Its matteness is adjustable by varying the amount of calcined kaolin (or simply blending in a glossy recipe to shine it up a little). The mechanism of the matteness is high MgO in a boron base of low Si:Al ratio.

Do not use regular kaolin, the glaze will shrink too much during drying.
Use enough water in the slurry so it flows well, it will apply very evenly without drips. If there is not enough water and the slurry is too creamy, it will crack during drying and crawl during firing. Calcine part of the Ravenscrag to reduce the shrinkage if needed.

The tin oxide is included to whiten and opacify the glaze, if you remove it the color will be quite a bit darker, especially on darker clay bodies (Ravenscrag contains some iron). The 1.5 wollastonite is a remnant of how this glaze was created; it started as Moores Matte, a well-known Gerstley Borate-based matte recipe. We first reformulated it to substitute the GB for a frit (while maintaining the same chemistry) and then incorporated Ravenscrag Slip to supply as much of the rest of the chemistry as possible. A further adjustment was made to make the surface more silky. The silky matte G2934 followed this, it being a cleaner, whiter variant having no Ravenscrag but the same fired surface.

Since this has some iron, colouring it with stains could produce more muddied colours than you might want. Consider using the G2934 base instead if needed.

Related Information

Ravenscrag Cone 6 silky matte does not work well on dark burning bodies

Like Plainsman M390 on the right. It is good on M340 (a buff stoneware on the left), but it is even better on a porcelain.

Comparing two glazes having different mechanisms for their matteness

These are two cone 6 matte glazes (shown side by side in an account at Insight-live). G1214Z is high calcium and a high silica:alumina ratio. It crystallizes during cooling to make the matte effect and the degree of matteness is adjustable by trimming the silica content (but notice how much it runs). The G2928C has high MgO and it produces the classic silky matte by micro-wrinkling the surface, its matteness is adjustable by trimming the calcined kaolin. CaO is a standard oxide that is in almost all glazes, 0.4 is not high for it. But you would never normally see more than 0.3 of MgO in a cone 6 glaze (if you do it will likely be unstable). The G2928C also has 5% tin, if that was not there it would be darker than the other one because Ravenscrag Slip has a little iron. This was made by recalculating the Moore's Matte recipe to use as much Ravenscrag Slip as possible yet keep the overall chemistry the same. This glaze actually has texture like a dolomite matte at cone 10R, it is great. And it has wonderful application properties. And it does not craze, on Plainsman M370 (it even survived a 300F-to-ice water IWCT test). This looks like it could be a great liner glaze.

Ravenscrag based silky MgO matte at cone 6

Cone 6 G2928C Ravenscrag Silky Matte on Plainsman M340 (left) and M370 (right). The inside of the M370 mug is a transparent glossy. This recipe produces a silky ivory-coloured surface of very good quality.

A functional matte liner glaze is possible - with care.

Ravenscrag G2928C matte liner glaze is on the insides of these mugs. Like our G2934 recipe, this matte glaze needs to be fired to a real cone 6 and fired in the C6DHSC drop and hold and then slow-cooled schedule. If cooled too slowly the surface could be too matte would be subject to cutlery marking (especially on the inside bottoms). If cooled too quickly it will be too glossy. When firings cool slowly just because they are tightly packed the degree of matteness can be tuned by blending in just enough glossy glaze to make the surface smooth enough to be functional while still matte enough to be attractive to the eye and the touch.

Links

Typecodes	Matte Glaze Recipes Much less common that glossy glazes, normally have stricter firing requirements.
Typecodes	Medium Temperature Glaze Recipes Normally fired at cone 5-7 in electric kilns.
Firing Schedules	Plainsman Cone 6 Electric Standard Used in the Plainsman lab to fire clay test bars in our small kilns
Glossary	Dolomite Matte Dolomite matte glazes have the potential to be very silky and pleasant to the touch, while at the same time being hard, durable and non-crazed (if they are formulated correctly).
Glossary	Matte Glaze Random material mixes that melt well overwhelmingly want to be glossy, creating a matte glaze that is also functional is not an easy task.
Media	How I Formulated a Cone 6 Silky Matte Glaze Using Insight-Live I will show you how found a recipe on Facebook, assessed it, substituted my own materials, tested it, adjusted it. Now it is like a cone 10 dolomite matte.
Recipes	G1214Z1 - Cone 6 Silky Matte This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte.
Recipes	G2934 - Matte Glaze Base for Cone 6 A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.
Recipes	GR10-C - Ravenscrag Cone 10R Silky Talc Matte Just Ravenscrag Slip plus 10% talc produces a visually variegated surface that feels silky and looks stunning!

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By Tony Hansen
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