Ravenscrag Slip


Fine grained low plasticity cone 10 melting silty clay. Ravenscrag Slip is a blend, its principal ingredient is mined from a large deposit near Ravenscrag, Saskatchewan, Canada. It was originally developed as an almost-complete base cone 10 glaze (it is feasible to use 'as is' on either green or bisque fired ware, to achieve a light colored silky matte surface). The material can be viewed as a 'plastic feldspar' that provides good melting and excellent slurry properties in a light colored material. In educational and beginning pottery settings it is an ideal starting-point for material-blending style glaze development and experimentation with colors, opacifiers, variegators and matting agents.

All of these mugs are made from glazes whose major component is either Alberta Slip or Ravenscrag Slip. They are all fired at cone 10R.

Process Properties

Pure Ravenscrag Slip has very good application properties. It resists crawling on sharp interior corners and edges. However, it contains significant clay and does shrink on drying. So in many cases, like Alberta Slip, it is good to use a blend of calcine and raw in recipes, especially for multi-layer application (check for information on how to calcine). It is also good to test to make sure that over layers do not 'pull' on the Ravenscrag Slip under-layer and compromise its dry-bond with the body.

Left: Raw Ravenscrag Slip powder. Right: Calcined at 1080F.

Since Ravenscrag Slip is a siltly material it does not work well for burnishing.


Ravenscrag Slip is the opposite of Alberta or Albany Slip: The latter is a low-melting, plastic, and dark burning; this is higher-melting, non-plastic, and light burning. It melts to a silky-matte surface at cone 10. demonstrates the addition of fluxes to get betting melting if needed.

Adding about 20% Ferro 3134 frit will produce a base transparent glaze for cone 6. You can add colorants (i.e. stains, metal oxides), variegators (i.e. 5% rutile), and opacifiers (i.e. 10% Zircopax) to create almost any effect.

Since it is basically a clay material a significant amount of gas is generated during decomposition during melting. If not fired high enough and not fluxed adequately very thick layers could tend to form unbroken bubbles in the glaze layer.

Glaze Recipes

For more detailed information go to

Physical Properties

 Drying Shrinkage: 3.5-4.5%

Sieve Analysis (Tyler mesh):

     +100: 0.0-0.1%
 100-150: 0.5-1.5
 150-200: 2.5-3.5
 200-325: 5.5-8.0

Chemical Analysis

 CaO      10.1
 K2O       3.0
 MgO       1.7
 Na2O      0.5
 TiO2      0.4
 Al2O3    12.6
 SiO2     61.8
 Fe2O3     0.8
 LOI       8.8%


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Alberta Slip/Ravenscrag celadon cone 6 on P300 and M340. By Tony Hansen.

H450 mugs fired at cone 10R with pure Alberta Slip on the outsides, G1947U transparent (left) and pure Ravenscrag Slip on the insides. By Tony Hansen.

This is 100% Alberta Slip (outside) and 100% Ravenscrag Slip inside. White stoneware H450 clay fired to cone 10R. Both glazes have been made using a blend of calcine and raw (60:40 and 50:50). By Tony Hansen.

Safety Data Sheet

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Logo Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX:403-527-7508