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Alberta Slip

Description


GA6-B, GR6-A glazes on M340 at cone 6 oxidation. These glazes are just Alberta Slip and Ravenscrag Slip with 20% added frit. Both of these apply well and fire to a brilliant surface with minimal defects if firings are slow cooled.


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 roast (60:40 and 50:50). By Tony Hansen.

Fine-grained, plastic, dark brown burning clay that melts to form glossy rich beanpot-brown glazes at high fire reduction (cone 10) and a glossy amber brown at cone 6 oxidation (with frit addition).

Historically, Albany Slip was a 'standard' within the North American pottery community and ceramic industry. It was a silty glacial clay that melted easily at high temperatures to form a 'natural glaze'. With additions of 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 dark coloring oxides and stains to produce deep blacks, browns and even blues. It produced glazes that had 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. We published the process we used to do it. Alberta Slip had the same chemistry and very similar firing properties (the original material was somewhat variable, we patterned our work after an average sample). 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.

Preparation


Left: Raw Alberta Slip powder. Right: Roasted at 1080F. This is a plastic clay, thus it has a significant drying shrinkage. Where a glaze is applied thickly or the percentage of Alberta Slip is high, shrinkage cracks (which produce crawling during firing) will occur. We recommend a mix of roast and raw material in recipes. Roasting the Alberta Slip powder at 1000F greatly reduces the shrinkage. Use a firing rate and hold-time-at-1000F appropriate for the wall thickness and size of your bisque vessels (e.g. 500F/hr and 30 minutes for thin walled small vessels, slower and longer hold for large ones). If any of the powder within is black, increase hold time. Adjust proportions as needed (more roast if the glaze cracks on drying or more raw if it is drying too powdery or not bonding well).

The roasted material has a weight-loss of about 3% on firing (vs. 9% for the raw powder). This difference can be ignored in most cases. But, to be more precise, use 3% less of the roasted powder (multiply the amount by 0.97). For example, suppose you need 1000 grams of a 50:50 raw:cacline Alberta Slip mix for a glaze recipe. Use 500 raw and 500*.97=485 roast.

Alberta slip is much more plastic than Albany was. This means that it dries much harder and less dusty but also has a higher drying shrinkage. If an Alberta Slip glaze cracks when drying then part of the material needs to be roasted (to cut shrinkage). While this sounds like an extra hassle, it affords control over slurry properties. With the right blend (e.g. 50:50 in a glaze having 80-100% Alberta Slip, the glaze suspends and applies well, dries hard and does not crack for normal thickness.

We roast it to 1000F, high enough to destroy the plasticity (firing higher than that could can calcine it, sintering particles together and creating grit). Use a firing rate and hold-time-at-1000F appropriate for the wall thickness and size of your bisque vessels (e.g. 500F/hr and 30 minutes for thin walled small vessels, slower and longer hold for large ones). Watch for black powder remaining in the center as an indication of insufficient roasting.

Adjusting percentages: This roasted material has an LOI of about 3% (vs. 9% for the raw powder). This difference can be ignored in most cases. But if you want to be more precise, use 3% less of the roasted powder (multiply the amount by 0.97). For example, suppose you need 1000 grams of a 50:50 raw:cacline Alberta Slip mix for a glaze recipe. Use 500 raw and 500*.97=485 roast. Then watch how the slurry performs and adjust the proportions if needed (more roast if the glaze cracks on drying or more raw if it is drying too powdery or not bonding well).


Alberta Slip is a plastic clay, if used in recipes in higher percentages, it can cause them to crack during drying. A mix of roast:raw must be used.

Process Properties

In our studio we use pure Alberta Slip as a glaze at cone 10R. We mix it using a 60:40 roasted:raw mix of Alberta Slip powder. Glazes are most often prepared using the traditional method of simply adding water until the desired consistency is achieved (rather than targeting specific gravities and conditioning with flocculants). This works well in recipes having a high percentage of Alberta Slip, the clay:roast mix (which you control) coupled with its predominance in the recipe creates a slurry that applies well across a range of viscosities without the help of any rheological chemicals. Care is needed for more viscous slurries, these tend to go on too thick. When frit is added to make it melt at lower temperatures, lower specific gravities (higher water content) will likely be needed. In recipes that have low percentages of Alberta Slip, calcining is likely not needed and they can be treated normally (gelled to a thixotropic state).

If multiple layers of Alberta-Slip-based glazes need to be applied, CMC Gum additions will be needed to prevent cracking and/or release from the bisque.

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 gas 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). For example, GA6-B produces a far better transparent for dark burning bodies like M390 or Coffee Clay.

Glazing

There are some coarser particles in the material so 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).

As a raw material, the plasticity of Alberta Slip makes it an ideal base for 'slip glazes' for use on leather-hard ware. These do not need to be made using a mix of roast and raw, the pure raw powder is better.

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

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.

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.

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%

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Gallery


Plainsman h450 (buff stoneware) 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.


Pure Alberta Slip GA6-B base on a porcelain at cone 6.


M340GS with GA6-B Alberta Slip base glaze. Cone 6.


M340 with Alberta Slip GA6-C rutile blue glaze. Cone 6. L3954B black engobe was applied inside and half way down the outside during leather hard stage.


P300 with L3500E base glaze (20% frit 3249, 80% Alberta Slip) to produce a low thermal expansion).


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


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.

Courtesy of Digitalfire Reference Library

Alberta Slip Cone 6 Amber Base Glaze

Code: GA6-A

An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares.

Alberta Slip 1000F Roasted40.00
Alberta Slip40.00
Ferro Frit 313420.00
100.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

This is the base cone 6 Alberta Slip recipe. The 20% frit makes it melt well to form a transparent amber glossy.

Frit 3134 has traditionally been used and it is the best for some additions (e.g. rutile for floating blue). However we recommend Frit 3195 when possible, it imparts a lower thermal expansion for better fit (less crazing). For use on P300 we recommend Ferro 3249 (or Fusion F-69) for the lowest possible thermal expansion.

This base can be used as-is (with no colorant or variegator additions). It is most useful to replace regular transparent glazes on dark-burning clays (to avoid issues with micro bubble clouding). If not cooled slowly, the effect is a very clean, speck free amber transparent glossy that showcases the dark body color below. On light-burning clays and even porcelains, celadon green effects can be produced.

However, if this glaze is cooled slowly (which often happens in heavily loaded kilns) it will form surface crystals. These can produce beautiful effects (depending on cooling speed) that normal clear glazes having added iron oxide powder will normally do. For consistency in appearance it will be necessary to program the descent of your firings to match the slowest natural descent you normally get. Then, on that baseline, you will be able to depend on consistent results. By adding 1% tin oxide you can prevent crystallization (see photo below).

This recipe is excellent base for additions and many of these are documented on the cone 6 glazes page at http://albertaslip.com. Glossy brown to black colors require much less stain than does a standard clear base glaze. Reactive rutile and titanium effects that depend on the presence of some iron also react really well with this base.

As noted above, assess the fit with your clay body to be sure there is no tendency to craze (by stressing ware using a 300F-to-icewater IWCT test ice). If crazing occurs switch to frit 3195 (GA6-B). If it still occurs (e.g. with a porcelain), switch to frit 3249. Note again: While these frits still produce the glossy amber transparent effect they may not react the same with colorants, especially the rutile blue.

Glazes having a high percentage of Alberta Slip are most often prepared using the traditional method of simply adding water until the preferred viscosity is achieved (the material has inherent properties that produce functional slurries for dipping). Control of drying shrinkage and slurry character is achieved by varying the proportion roast and raw powder in the recipe. For us, a weight ratio of 88 water to 100 powder (2200 water for 2.5kg of powder) produces a 1.45-specific-gravity slurry that, although fairly runny, gives the right thickness on 1-2 second dip on 1850F bisque-ware (there is some dripping, but coverage is even and it is quick drying). This recipe actually does not respond to flocculant additions that gel traditional mineral-blend glazes to a thixotropic state.

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

A transparent that looks good on cone 6 red burning bodies

The GA6-A Alberta Slip:Frit 3134 (80%:20%) glaze is excellent as a liner for dark burning bodies, it looks much better than a regular transparent recipe (which often form clouds of bubbles on red bodies). The iron in this glaze makes it fire an amber color on buff burning bodies (not very attractive), but on red bodies it brings out the natural color of the clay.

A cone 6 clear glaze plus iron vs. Alberta Slip amber base

These two mugs are made from a dark red burning stoneware and fired in a cool-and-soak firing schedule. A white engobe (L3954A) has been applied on the inside and half way down the outside. Both are glazed inside with G2926B whiteware transparent glaze. The outside glaze on the left is the same transparent with 4% added iron oxide. It has been sieved to 80 mesh. Notice the iron agglomerates and still produces specking (an effect that may be desired, but difficult to keep consistent). Interestingly, that iron is producing a clear amber-colored glass about equal in color to the Alberta Slip GA6A base glaze (80% Alberta Slip, 20% Frit 3195) on the mug on the right. Neither has the micro bubbles that mar a typical clear glaze on bodies like this.

A Cone 6 white engobe works miracles on these dark and buff burning bodies

Left is Plainsman M340. Right is M390. Each mug has been white engobed inside and half-way down the outside. The insides have been glazed using G2926B clear. The inside surface has more depth and has a richer appearance than you could achieve using a white glaze (especially over the dark burning body). The outside of the left one is Alberta Slip base GA6A using Frit 3195 (it produces a more stable glass of lower thermal expansion). The outside glaze on the right is the clear plus 4% iron oxide. This technique of using the engobe enables porcelain-like functional surfaces on the insides and striking visual contrast and character on the outside of the dark body mug.

GA6A Alberta Slip base using Frit 3249 and 3195 on buff body

The body is buff burning Plainsman M340 (cone 6). The amber colored glaze is 80% Alberta Slip (raw:calcine mix) with 20% of each frit. The white engobe on the inside of mug 1 is L3954A (also glazed inside using transparent G2926B). These frits are producing an amber gloss glaze of high quality. On the outside of mug 1 we see the 3195 version on the white slip until midway down, then on the bare buff clay (the other has the 3249 version). These mugs are fired using a drop-and-soak firing schedule. There is a caution: Frit 3249 has a very low thermal expansion, use it on bodies that craze other glazes (like Plainsman P300), it could shiver on stonewares like this.

Plainsman iron red clays with rutile blue Alberta Slip glaze

Cone 6 mugs made from Plainsman M350 (left) and M390 dark burning cone 6 bodies. The outside glaze is Alberta-Slip-based GA6-C rutile blue and the inside is GA6-A base (20% frit 3134 and 80% Alberta Slip). That inside glaze is normally glossy transparent amber, but crystallizes to a stunning silky matte when fired using the C6DHSC schedule.

Tin oxide stops crystallization in GA6-A Alberta Slip base glaze

Both of these mugs were soaked 15 minutes at cone 6 (2200F), then cooled at 100F per hour to 2100F and soaked for 30 minutes and then cooled at 200F/hour to 1500F. This firing schedule was done to eliminate glaze defects like pinholes and blisters. Normally the GA6-A glaze crystallizes (devitrifies) heavily with this type of firing, but an addition of 1% tin oxide to the one on the left has prevented this behavior.

GA6A Alberta Slip base using Frit 3124, 3249 and 3195 on dark body

The body is dark brown burning Plainsman M390 (cone 6). The amber colored glaze is 80% Alberta Slip (raw:calcine mix) with 20% of each frit. The white engobe on the inside of two of the mugs is L3954A (those mugs are glazed inside using transparent G2926B). The Alberta Slip amber gloss glaze produces an ultra-gloss surface of high quality on mugs 2 and 3 (Frit 3249 and 3195). On the outside we see it this glaze on the white slip until midway down, then on the bare red clay. The amber glaze on the first mug (with Frit 3124) has a pebbly surface. These are fired using a drop-and-soak firing schedule. Some caution is required with the 3249 version, it has low thermal expansion (that is good on bodies that normally craze glazes, but risks shivering on ones that do not).

A typical transparent glaze vs. Alberta Slip amber base vs. a on a red burning cone 6 body

The body is Plainsman M332, a coarse particled brown to red burning cone 6 body. With the G2926B transparent cone 6 glaze (left) and the GA6-A Alberta Slip base (right). The latter brings out the color of the body much better, the former is milky, bubbly and yucky!

Fast cooling vs. slow cooling Alberta Slip GA6-A transparent base

These two mugs have the Alberta Slip base cone 6 GA6-A glaze on the inside. The left one is cooled normally (kiln off at cone 6 after soak). For the mug on the right the kiln has been soaked for half an hour at 1800F on the way down. This was done to develop the rutile blue glaze on the outside, but during this period crystallization occurred on the inside. If you need to cool slow (for the Alberta Slip rutile blue) but would like the transparent liner, add 0.5-1% tin oxide to the GA6-A to impede crystal growth.

Same glaze, same kiln, same clay: The right one crystallized. Why?

Well, actually they are not exactly the same. This is 80% Alberta Slip and 20% frit. But the frit on the left is Ferro 3195 and on the right is 3134. By comparing the calculated chemistry for these two we can say that the likely reason for the difference is the Al2O3 content. Frit 3134 has almost none whereas 3195 has 12%. Al2O3 stiffens the glaze melt, that impedes crystal growth. But it stabilizes the melt against running during firing. Frit 3195 has more boron, so the one on the left should be running more. But it actually runs less. Why? Again, because the increased Al2O3 is stiffening the melt.

 


Alberta Slip Cone 6 Black

Code: GA6-H

Pure Alberta Slip can be made into a black adding only 20% frit and 3% black stain

Alberta Slip 1000F Roasted33.00
Alberta Slip40.00
Ferro Frit 313420.00
Add
Zircopax4.00
Mason 6666 Black Stain3.00
100.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

A glossy black. The small amount of frit needed is due to the fact that Alberta slip is a dark burning material already. If it is not black enough, increase the percentage of stain. If you need a glossier surface, increase the frit. If it crazes switch to Ferro Frit 3195. Should be ball milled.

For mixing instructions please see the master recipe, GA6-A.

This one inch tall mug was made using Alberta Slip plus 1% black stain and 20% frit 3134.

Ravenscrag Black on Plainsman M340

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

 


Alberta Slip Cone 6 Oatmeal

Code: GA6-F

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

Alberta Slip 1000F Roasted40.00
Alberta Slip40.00
Ferro Frit 313420.00
Add
Rutile5.00
Titanium Dioxide3.00
108.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

Alberta slip is well suited to oatmeal glazes because it already has the iron content needed. Vary the titanium for more or less gloss and oatmeal appearance.

This glaze is very attractive, but one issue you might encounter is pinholing or blistering if it is too thick (a common problem with this type of glaze). Try using it on different bodies and thicknesses to find the best combination. Adjust the frit if you would like it to melt lower or higher. Do not hesitate to reduce the rutile and titanium by a percent to experiment. Getting this glaze working is well worth the effort, not just for the fired results, but for how well it works in the studio. It is actually less troublesome than most others that fire similarly.

This recipe was referred to as GA6-B in past.

For mixing instructions please see the master recipe, GA6-A.

How much rutile can a glaze take before it becomes unstable?

The 80:20 base Alberta slip base becomes oatmeal when over saturated with rutile or titanium (left:6% rutile, 3% titanium; right:4% rutile, 2% titanium right). That oatmeal effect is actually the excess titanium crystallizing out of solution in the melt as the kiln cools. Although the visual effects can be interesting, the micro-crystalline surface is often susceptible to cutlery marking and leaching. This is because the crystals are not as stable or durable as the glass of the glaze.

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

 


Alberta Slip Glossy Brown Cone 6

Code: GA6-D

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

Alberta Slip 1000F Roasted40.00
Alberta Slip40.00
Ferro Frit 313420.00
Add
Rutile4.00
Tin Oxide4.00
108.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

Works well on all types of bodies, very reliable.

For mixing instructions please see the master recipe, GA6-A.

Tin oxide can stop the rutile variegation effect dead in its tracks!

This is Alberta Slip (GA6C) on the left. Added frit is melting the Alberta Slip clay to it flows well at cone 6 and added rutile is creating the blue variegated effect (in the absence of expensive cobalt). However GA6D (right) is the same glaze with added Tin Oxide. The tin completely immobilizes the rutile blue effect, it brings out the color of the iron (from the rutile and the body).

GA6-D brown Alberta Slip glaze at cone 5R.

Variegating effect of sprayed-on layer of 100% titanium dioxide

The referred to surface is the outside of this large bowl. The base glaze (inside and out) is GA6-D Alberta Slip glaze fired at cone 6 on a buff stoneware. The thinness of the rutile needs to be controlled carefully, the only practical method to apply it is by spraying. The dramatical effect is a real testament to the variegating power of TiO2. An advantage of this technique is the source: Titanium dioxide instead of sourcing TiO2 from the often troublesome rutile.

Speckled GA6-D glaze at cone 6.

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

 


Alberta Slip Lithium Brown Cone 6

Code: GA6-G

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

Alberta Slip40.00
Alberta Slip 1000F Roasted35.00
Ferro Frit 319521.00
Lithium Carbonate5.00
Alumina Hydrate5.00
Add
Tin Oxide4.00
110.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

One of the most popular Albany Slip glazes was 11% lithium, 4% Tin and 85% Albany Slip. A portion of the Alberta Slip must be milled or the glaze will crack during drying.

This recipe reduces the lithium to reduce shivering problems (that were common with this) and it employs a frit to help melt the glaze. The surface is very smooth and variation in color with thickness is very good. The added alumina hydrate darkens the color and slightly dulls the very glossy nature of the recipe, you can leave it out if you want.

Visually, this glaze works very well on porcelain showing variegated effects even on smooth surfaces, especially where very thinnly applied. However it crazes on porcelains, please use the alternate lithium brown recipe.

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

Alberta Slip using in the common lithium-tin cone 6 glaze

This is 85% Alberta Slip, 11% lithium and 4% tin fired at cone 6 in oxidation. Like the original Albany version, it has a very low thermal expansion (because of the high lithium content) and likes to shiver on many bodies.

A variation of Albany lithium brown glaze

Alberta Slip 75, lithium carbonate 10, tin oxide 4, nepheline syenite 11, calcined alumina 5.

A classic Albany glaze that often shivers

These mugs have experienced very serious shivering. This is an Albany Slip glaze with 10% lithium carbonate, it is known to have a very low thermal expansion. This problem can be solved by reducing the amount of lithium or adding high-expansion sodium or potassium. However these fixes will likely affect the appearance.

A closeup of Alberta Slip lithium brown cone 6 recipe GA6-G on a porcelain

This has been applied very thinly, yet still covers very well and exhibits alot of variation even where thicknesses are slightly different.

 


Alberta Slip Lithium Brown Cone 6 Low Expansion

Code: GA6-G1

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

Alberta Slip40.00
Alberta Slip 1000F Roasted35.00
Ferro Frit 324917.00
Silica4.00
Lithium Carbonate4.80
100.80

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

The regular Alberta Slip lithium brown recipe crazes on porcelain. This one was formulated to maintain the appearance but reduce the thermal expansion. It does this by reducing the KNaO and increasing the MgO. This was effected by employing MgO sourcing frit 3249. This frit is more expensive and difficult to get but it is the only way we have found to effectively reduce the thermal expansion and maintain the aesthetic.

Like the original albany glaze, this recipe contains lithium carbonate (which is partially soluble), thus the slurry can gel over time. This necessitates the addition of water and increases the drying shrinkage and there cracking (which results in crawling). We are working on substituting a lithium frit to eliminate this issue.

For mixing instructions please see the master recipe, GA6-A.

Some glazes look great on red clay and horrible on white

Alberta Slip cone 6 lithium brown (GA6-G1) on a red burning clay (left Plainsman M390) and buff burning (right M340). Obviously this looks better on the former where iron from the underlying body variegates the entire surface and bleeds through on contours where the glaze is thinner, creating a breaking effect.

Fine tuning glaze shrinkage vs. hardness

These mugs are fired at cone 6 with GA6-G1 Alberta Slip lithium brown. The difference: the ratio of raw to calcine Alberta Slip. In this glaze, a 50:50 ratio was not working well (left). The glaze was shrinking too much on drying, then crawling on firing (it needs to be thickly applied to get the visual effect I want). I mixed the recipe using pure calcine Alberta Slip, then repeated a cycle of pouring a little of this into the 50:50 mix and trying it. I kept doing that and glazing another mug until I had a minimum of drying cracks (while still having good gelling, application properties and dry hardness). The mug on the right was the last cycle, it has fired perfect. Using this technique I can perfect the ratio of raw:calcine for each Alberta Slip glaze I use.

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

 


Alberta Slip Rutile Blue Cone 6

Code: GA6-C

Plainsman Cone 6 Alberta Slip based glaze the fires bright blue but with zero cobalt.

Alberta Slip 1000F Roasted40.00
Alberta Slip40.00
Ferro Frit 313420.00
Add
Rutile4.00
104.00

The firing schedule may be important to developing this glaze effect.
Cone 6 Standard Firing Schedule
Cone 6 Slow Cool Firing

This glaze creates a bright blue yet contains none of the world's most expensive common ceramic material, cobalt oxide. It has a great glossy surface and variegates a from medium steel blue where it is very thick to amber clear (or a brown if the body is dark) where it is too thin.

You will need to experiment to get it the right thickness in your circumstances. Try it on different clays and different thicknesses to find the best combination. It works best on stonewares. If it is melting too much or too little, increase or decrease the frit to compensate.

One possible caution: This glaze relies on the rutile variegation effect. Rutile can vary in chemistry over time and from place to place, so test this first before using and test it again when you get new supplies of rutile.

THE FLOW COLORATION REQUIRES SLOWER COOLING. This can happen naturally if you fire packed loads or have a well insulated kiln, but it is generally best to program the cool (use the Slow Cool schedule link to learn more, it drops the temperature, then holds, then slows the cooling to about 1400F). You can also add 0.25% cobalt oxide to restore the color if you want to do a faster cool (to prevent transparent glazes clouding, for example)! If the blue is working, but less than you want, then add a little less cobalt.

If the glaze shrinks and cracks too much on drying, then increase the calcine Alberta Slip and reduce the raw Alberta Slip. If it is too powdery on drying, increase the raw against the calcine.

There is also a Ravenscrag Slip version of this glaze, it employs iron, cobalt and rutile (like the original David Shaner recipe).

Roasting Alberta Slip at 1000F

Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about one kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages of Alberta Slip. And 1000F? Calcining to 1850F sinters some particles together (creating a gritty material) while 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

The rutile mechanism in glazes

2, 3, 4, 5% rutile added to an 80:20 mix of Alberta Slip:Frit 3134 at cone 6. This variegating mechanism of rutile is well-known among potters. Rutile can be added to many glazes to variegate existing color and opacification. If more rutile is added the surface turns an ugly yellow in a mass of titanium crystals.

Close-up of Floating Blue on cone 6 dark/buff burning bodies

Originally popularized by James Chappell in the book The Potter's Complete Book of Clay and Glazes. It is loved and hated. Why? The high Gerstley Borate content makes it finicky. But the magic ingredient is not the GB, it is the rutile, Rutile makes the cobalt and iron dance. This recipe actually produces a number of different mechanisms of variegation. Color and opacity vary with thickness. Small rivulets of more fluid glass flow around more viscous phases producing micro-areas of differing colors and opacities. Titanium crystals sparkle and calcium-borate creates opalescence. Bubbles of escaping gases (from GB) have created pooling. Small black speckles from unground or agglomerated particles of iron are also present. Surprise! This is actually Ravenscrag Floating blue. All the visuals, none of the headaches.

Deep, deep blue without any cobalt. How?

These have to be seen to be believed, it is the deepest, richest blue we have ever produced. This is Plainsman M340 fired to cone 6. Black-firing L3954B engobe (having 10% Burnt (not raw) Umber instead of the normal 10% Zircopax) was applied inside and partway down the outsides (at the stiff leather hard stage). The incising was done after the engobe dried enough to be able to handle the piece. The glaze is Alberta Slip rutile blue. Firing schedule: Cone 6 drop-and-soak.

Ravenscrag Floating Blue vs. Alberta Slip Rutile Blue

Cone 6 oxidation. GR6M Ravenscrag version is on the left. The Alberta Slip version (GA6C) is more fluid, but that also means it will run more during firing and blister more if too thick or on re-firing. Generally, the Alberta Slip version appears better on dark bodies and the Ravenscrag one on lighter burning clays. The Alberta Slip version gets its color only from Rutile (and thus requires a special drop-and-hold firing scheduel), the Ravenscrag one produces blue in any firing schedule (although the color will be better in the drop-and-hold schedule).

Alberta Slip Rutile-blue needs Frit 3134, it does not work with others

These two cone 6 mugs have the same glaze recipe: GA6A Alberta Slip base. 4% rutile has been added to each. They were fired in the same kiln using a slow cool schedule. The recipes and chemistry are shown below (the latter gives a clue as to why there is no blue on the right). The mug on the left is the traditional recipe, 80:20 Alberta Slip:Ferro Frit 3134. Frit 3134 melts at a very low temperature and a key reason for that is its near-zero Al2O3 content. Al2O3 in glazes stiffens the melt and imparts durability to the fired glass (normally we want adequate levels in functional glazes). When Al2O3 levels are low and cooling is slower molecules in the stiffening glass have much more freedom to move and orient themselves in the preferred way: crystalline (fast cooling produces a glass). Thus the rutile in the glaze on the left has had its way, dancing as the kiln cooled, producing all sorts of interesting variegated visual effects. The glaze on the right employs Ferro Frit 3195. It has lots of Al2O3 and has contributed enough to stop the rutile dead.

Rutile blue glaze effect completely lost! A temporary solution.

Left: 4% rutile in the Alberta Slip:frit 80:20 base. This glaze has been reliable for years. But suddenly it began firing like the center mug! Three 5 gallon buckets of glaze (of differing ages) all changed at once. We tried every combination of thickness, firing schedule, clay body, ventilation, glazing method on dozens of separate pieces with no success to get the blue back. Even mixed a new batch, still no color. Finally the 'crow bar' method worked, 0.25% added cobalt oxide (right mug). It is identical ... amazing. It is not the same mechanism to get the color and it is not exactly the same, but worked while we figured out the real issue: the firing schedule (the secret turned out to be cooling, soaking, then slow cooling to 1400F).

Plainsman iron red clays with rutile blue Alberta Slip glaze

Cone 6 mugs made from Plainsman M350 (left) and M390 dark burning cone 6 bodies. The outside glaze is Alberta-Slip-based GA6-C rutile blue and the inside is GA6-A base (20% frit 3134 and 80% Alberta Slip). That inside glaze is normally glossy transparent amber, but crystallizes to a stunning silky matte when fired using the C6DHSC schedule.

The classic cone 6 floating blue? No, it is Alberta Slip blue.

And it contains no cobalt! Fairly close in appearance to the classic cone 6 Floating Blue recipe used across North America, this is a variation of the Alberta Slip Rutile Blue glaze (except this adds 1% tin oxide, 1% black copper oxide and 2% ceramic rutile, it is GA6-C1). Because of the melt fluidity, it thins on the edges of contours and breaks to the color of the underlying body. It looks best on dark bodies, but if thick it is OK on light ones also.

Adding spodumene to this floating blue tones down the white patches

GA6-C (left) and GA6-E (right) at cone 6 oxidation. The E version adds 4% spodumene onto the 4% rutile in the C (the base is 80% Alberta Slip and 20% frit 3134). The spodumene eliminate the overly whitish areas that can appear. This glaze requires the "Slow Cool (Reactive Glazes)" firing schedule. It looks the best on dark bodies.

Alberta Slip rutile blue on a porcelain (left) and buff stoneware (right)

The recipe is GA6-C. These are from the same firing (slower cooling is needed to develop the rutile effect).

GA6-C Alberta Slip rutile blue at cone 5R

On Plainsman P300 (left) and M350 (right). The blue effect is darker and richer than oxidation. The richer effect is also partly because the reduction kiln cools slower.

Tin oxide can stop the rutile variegation effect dead in its tracks!

This is Alberta Slip (GA6C) on the left. Added frit is melting the Alberta Slip clay to it flows well at cone 6 and added rutile is creating the blue variegated effect (in the absence of expensive cobalt). However GA6D (right) is the same glaze with added Tin Oxide. The tin completely immobilizes the rutile blue effect, it brings out the color of the iron (from the rutile and the body).

MgO can destroy the rutile blue variegation effect

The rutile blue variegation effect is fragile. It needs the right melt fluidity, the right chemistry and the right cooling (during firing). This is Alberta Slip GA6C recipe on the right (normal), the glaze melt flows well due to a 20% addition of Ferro Frit 3134 (a very low melting glass). On the left Boraq has been used as the flux (it is a calcium borate and also melts low, but not as low as the frit). It also contains significant MgO. These two factors have destroyed the rutile blue effect!

Alberta Slip Rutile blue glaze too thin on a dark body

This mug has thin walls and was bisque fired to cone 04 (so it had a fairly porosity). As a result the glaze went on thinner when it was dipped. This was not evident at the time of glazing but at firing the thinner sections produced the brown areas.

Cone 6 rutile floating blue effect lost. Then regained.

Left: What GA6-C Alberta Slip rutile blue used to look like. Middle: When it started firing wrong, the color was almost completely lost. Right: The rutile effect is back with a vengeance! What was the problem? We were adjusting firing schedules over time to find ways to reduce pinholing in other glazes and bodies. Our focus was slowing the final stages of firing and soaking there. In those efforts the key firing phase that creates the effect was lost: it happens on the way down from cone 6. This glaze needs a drop-and-soak firing (e.g. cooling 270F from cone 6, soaking, then 150F/hr drop to 1400F).

Ravencrag rutile blue vs. Alberta Slip floating blue at cone 6

Both have been applied at moderate thickness on Plainsman M325 (using a slurry of about 1.43-1.45 specific gravity, higher values end up getting them on too thick). The Ravenscrag version highlights contours better (the edges are black because of the black engobe underneath). It also produces the blue color whether or not the kiln is slow cooled to 1400F (although a faster cool is less blue). But the Alberta Slip version has zero cobalt so is less expensive to make. It produces a deeper color over the black engobe underneath the upper section of the pieces. Both of these produce a wide range of effects with different thickness, bodies and firing schedules.

 

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