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Alberta Slip

Description

Low temperature, fine-grained, medium plastic, dark brown burning clay that melts to form glossy rich beanpot brown slip glazes at high fire reduction (cone 10) and a glossy transparent brown glaze around cone 6 oxidation (with a 20% boron frit addition e.g. Ferro 3134).

Albany Slip was long a 'standard' within the North American pottery community. It was a silty glacial clay that melted easily at high temperatures to form a 'natural glaze'. With a little frit, feldspar, lithium carbonate, or gerstley borate, it produced a wide range of earth tone glazes in middle fire oxidation. Albany Slip responded well to coloring oxides and stains to produce deep blacks, browns and even blues and it produced a low thermal expansion (to avoid crazing). At cone 10R with only a small iron addition excellent tenmoku surfaces were possible. In the late 1980s Hamill and Gillespie Co. discontinued Albany Slip leaving thousands of users with less than ideal alternatives.

In 1988 we formulated Alberta Slip as the first widely available substitute material and published the process we used to do it. It had the same chemistry and very similar firing properties as an average sample of Albany Slip (the material was somewhat variable). Alberta Slip has been proven over many years and is used by people across North America to make many stunning glazes. Other substitutes have appeared from time to time but no others have had the success of this material.

Alberta Slip has its own website at http://albertaslip.com, it has lots of recipes and pictures and instructions on how to roast (or calcine) it (it is a must-read for all users). Digitalfire.com also has an article about how it was formulated and an information page.

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

In our studio we use pure Alberta Slip as a glaze at cone 10R. We mix it using equal weights of water and a 60:40 roasted:raw mix of Alberta Slip powder. This produces a specific gravity of about 1.40. We then add Epsom Salts to gel the mix slightly, this provides the best application properties (this must be done carefully in order to no over-gel). To make a more viscous slurry we use about a mix of about 90:100 water:powder, this produces a specific gravity of about 1.45. This applies well without needing to be gelled, but it can go on too thick (and more dripping will occur).

Firing

Like classic Albany Slip, Alberta Slip begins melting at middle temperatures and by cone 10 it produces a glossy brown in oxidation and a tenmoku in reduction. One of the major advantages of this material is the ease with which it can be adapted to different temperatures. 20% frit produces very good melting at cone 6 and 50% melts at cone 06.

Since it is basically a clay material, it generates a significant amount of gases as it decomposes during melting. However despite this it can produce stunningly smooth and defect-free surfaces (we do not have a good explanation for this).

Glazing

There are some coarser particles in the material so always sieve your glazes through 80 mesh or finer before use (the increased effort to screen finer than 80 mesh is not generally worth the trouble).

Since Alberta Slip is a plastic clay it dries hard but has an associated shrinkage, that means you may need to roast part of the Alberta Slip powder (see the preparation page at AlbertaSlip.com for details). As a raw material its plasticity makes it an ideal base for 'slip glazes' for use on leather-hard ware.

Like Albany Slip, Alberta Slip has a low thermal expansion. Thus glazes will tend to be craze free. Glazes having significant lithium carbonate can lower the expansion enough to produce shivering. Using this with materials containing high K2O/Na2O can produce glazes that craze (especially on porcelains).

Our melt flow tests show that Alberta Slip displays the same characteristic blistering as Albany in fast firings, however, it does not melt quite as vigorously (although it does flow as well). In addition, Alberta slip is not as inherently fine and silty as Albany. Alberta slip will tend to gel glaze suspensions a little more than Albany did and it does not deflocculate easily.

Glaze Recipes

A range of glaze recipes for Cone 10 and 6 can be found at this material's dedicated web site: AlbertaSlip.com.

Since Alberta Slip fires by itself to a dark gloss at cone 10, it is an ideal base for dark shiny colors (requiring the help of a flux at lower temperatures). Alberta Slip provides one of the best ways to create difficult-to-make black glazes. As little as 2-5% combined cobalt oxide, copper oxide, black stain, etc. can be employed to make range of excellent glossy blacks. The more fluid the glaze (i.e. more frit) the more the likelihood of crystalline effects. Saturating the color can produce gunmetal blacks.

This is a clay, if used raw in high percentages, it can crack during drying

In the past variegated crystal green glazes were made with addition of around 5% rutile to Albany Slip (and frit if needed). This works also with Alberta slip. The classic cone 6 variegated brown recipe using Albany with 10 lithium carbonate, 5% tin works well with Alberta Slip.

Visit the following page for information on variegating, opacifying and coloring glazes: Variegating Glazes.

Physical Properties

 Drying Shrinkage: 5.0-6.0%

Melt Flow:

 Cone 6: 3.0-4.0 cm
 Cone 8: 5.0-6.0 cm
 Cone 10: 7.0-8.0 cm

Sieve Analysis (Tyler mesh):

     +100: 0.0-0.1%
 100-150: 0.3-0.6
 150-200: 1.5-2.5
 200-325: 4.5-6.0

Chemical Analysis

The analysis of this material has changed in 2013, not because the material changed, but because we have switched to an actual assay for a calcuated analysis.

 CaO       5.9
 K2O       3.5
 MgO       3.9
 Na2O      2.2
 TiO2      0.3
 Al2O3    15.2
 P2O5      0.1
 SiO2     53.54
 Fe2O3     4.5
 LOI       9.2%

Downloads

  • Brochure for double-sided printing (uncheck the Fit to Page checkbox when printing or it will be too small)

Gallery

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.

Pure Alberta Slip GA6-A base on a porcelain at cone 6. However this one employs Ferro Frit 3195 instead of the normal Frit 3134.

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
Email: plainsman@telus.net