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Alberta Slip

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 been 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. 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.

The way in which the substitution was done is documented and educational (from a chemistry, mineralogical, physical and practical viewpoint). You can find more information here and here..

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. It is thus an ideal base for 'slip glazes' that are used on leather-hard ware and must shrink with the piece (the book The Magic of Fire has a chapter on the principles of making slip glazes).

The plasticity of Alberta Slip is a key advantage it has over traditional Albany Slip. Mixing raw and calcined material in the needed proportion makes it shrinkage-adjustable, it can be made to fit any application need or body. You can calcine Alberta Slip powder by firing the powder in a bisqued container to red heat and holding for 15 minutes (the calcined material has the same chemistry but no drying shrinkage). Used pure, Alberta Slip is ideal for slips that are applied to leather hard ware, however on bisque ware it will peel during drying. Start by using half raw and half calcined Alberta Slip (adjust the ratio as needed to get a compromise between needed hardness and tolerable shrinkage).

Like Albany Slip, Alberta Slip has a low thermal expansion. Thus glazes will tend to be craze free. However, if you use significant lithium carbonate as a flux with this material, be advised that it can shift the already low expansion enough to produce shivering, a hazardous situation for both user and maker alike.

Our 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

Since Alberta Slip is already dark glossy firing, it is an ideal base for dark shiny colors because less colorant is needed. It can be used 'as is' for high temperature glossy brown glazes and with small additions of flux (i.e. 15% frit 3134, or 20-30 feldspar or nepheline, or 5-10% Gerstley borate) it works well down to cone 6 or lower. Since the dark color is an important reason for using Alberta Slip it is best to dilute it with as little flux as possible.

Alberta Slip provides one of the best ways to create difficult-to-make black glazes. As little as 2-5% cobalt oxide, copper oxide, black stain, etc. can be employed to make range of excellent glossy blacks. Tom Coleman, for example, uses 30% nepheline syenite and 4.5% cobalt carbonate for a satin cone 10 black. The more fluid the glaze (i.e. more frit) the more the likelihood of crystalline effects. If minimum melter is used gunmetal black glazes can be achieved.

In the past variegated crystal green glazes were made with addition of around 5% rutile (and frit if needed). This works also with Alberta slip.

A classic cone 6 variegated brown recipe used Albany was 10 lithium carbonate, 5% tin, and 85% Albany. This works well with Alberta Slip, however like Albany, it can shiver on some bodies. You might try substituting some boron frit for some of the lithium or use a body of lower thermal expansion.

Getting a Sample

On our home page, please click on "dealers" for a listing of where Plainsman Clays can be purchased. In the US please contact The Archie Bray Foundation for a listing of Alberta Slip suppliers in your area.

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

 CaO       6.5
 K2O       3.0
 MgO       3.1
 Na2O      2.2
 TiO2      0.4
 Al2O3    13.8
 P2O5      0.1
 SiO2     56.8
 Fe2O3     4.1
 FeO       0.7
 MnO       0.0
 LOI       9.3%

MSDS

A detailed Materials Safety Data Sheet (MSDS) is available for this material. To view it Click Here. To download the Acrobat file to your computer, Right-Click Here for Windows or Hold-Click Here for Macintosh. A menu should pop-up that will give you an option to download the file.