|Monthly Tech-Tip |
Alternate Names: Ravenscrag Slip Calcined
Description: Silty fusible low iron clay
The chemistry of this material is slightly different than for raw Ravenscrag Slip (it does not lose any weight on firing, so it supplies more of each of the oxides to the fired glaze, 9% more). This chemistry provided here assumes complete calcination (to at least cone 04). However there is an issue. The page at ravenscrag.com recommends roasting to only 1000F, at that temperature it looses only 3% weight on firing.
Another issue is particulates. When calcined at 1900F, particles sinter together into larger ones, requiring glaze ball milling. But at 1000F this does not occur.
The clays are Plainsman H450 and H550. Firing is cone 10 reduction. A 50:50 mix of roasted and raw Ravenscrag slip was used. L3954N black engobe was applied at leather hard stage (on the insides and partway down the outsides). We call this recipe GR10-C Ravenscrag Talc Matte, it is on the insides of both and on the outside of the one on the left. The outside of the other is G2571A Bamboo, it is also an excellent matte base. The silky matte surfaces produced by these two are both functional (they are very durable and do not stain or cutlery mark). And they are very pleasant to the touch.
Ravenscrag web site
Ravenscrag Data Sheet at Plainsman Clays
Clays that are not kaolins, ball clays or bentonites. For example, stoneware clays are mixtures of all of the above plus quartz, feldspar, mica and other minerals. There are also many clays that have high plasticity like bentonite but are much different mineralogically.
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.
Ravenscrag Slip 1000F Roast
|By Tony Hansen|
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