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Ravenscrag Silky Matte for Cone 6

Code: G2928C
Modification Date: 2016-09-30 22:54:05
Member of Group: RV6

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

MaterialAmountPercent
Ferro Frit 313411.010.0%
Talc8.07.2%
Ravenscrag Slip60.054.3%
Nepheline Syenite13.011.8%
Wollastonite1.51.4%
Calcined Kaolin12.010.9%
Additions
Tin Oxide5.04.5%
 110.50  

Firing Schedule

Rate (F)Temp (F)Hold (Min)Step
100220601
300173302
1082175153
1502075304

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.

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

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.

Compare two glazes having different mechanisms for their matteness

Compare 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 (you can find more about it by googling 1214Z). 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 and 300F to ice water plunge without cracking). This looks like it could be a great liner glaze.

Ravenscrag based silky MgO matte at cone 6

Ravenscrag based silky MgO matte at cone 6

Cone 6 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. Go to Ravenscrag.com for more info.

A matte and a glossy liner glaze

A matte and a glossy liner glaze

Left: Ravenscrag G2928C matte on inside of mug. Right: A clear glossy. The matte needs to be soaked in the kiln long enough to make sure it develops a functional surface, especially on the bottom. Mattes are not always the best choice for food surfaces, but you can do it if you blend in enough glossy glaze to make it smooth enough not to cutlery mark.

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By Tony Hansen

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