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Cone 6 Alberta Slip Glazes

This is not a glaze recipe page. Alberta Slip is a glaze material, these are demonstration recipes of what can be done with it.

These are "not guaranteed-to-work glazes". This page focusses on the value of this material to make base glazes and provides some examples of variations. However circumstances differ, do testing and alter for your situation (for information on variegating, opacifying and coloring glazes click here).

Care should be taken not to fire glazes too fast or at too low of a temperature. Witness cones are recommended to assure you have reached cone 6. These glazes have worked in our studio at Plainsman Clays but we recommend testing them in your circumstances and on your clay bodies for fit.

For functional glaze, consider testing for leaching, crazing and cutlery marking.

Courtesy of Digitalfire Reference Library

Alberta Slip Cone 6 Amber Base Glaze

Code: GA6-A

An amber-colored transparent glaze that works better on brown and red burning stonewares than typical transparent glazes.

Alberta Slip Calcined40.00
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, it fires as a transparent amber glass. This is an excellent base glaze for many dark colors. It is also an excellent liner glaze for dark-burning clays (it looks better than a transparent) and amber glossy for light-burning clays.

If crazing occurs (you need to look closely for it) switch to frit 3195 or 3249 (however these frits may not react the same with colorants, especially the rutile blue).

In our lab we can make 1 Canadian gallon using a mix of 2700 water and 3000 dry (1200 Alberta Slip, 1200 Calcined Alberta Slip, 600 Frit). This produces a specific gravity of 1.45 at about the right viscosity for dipping. We add a 1-2 grams of Epsom Salts to this to gel the slurry a little for better application properties. A 1-2 second dip in 1850F bisque ware produces the right thickness. You can use alot less water and it will still be fluid, but it will go on too thick and cracking will occur.

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.

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!

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 that is not working nearly as well. These mugs are fired using a drop-and-soak firing 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.

Alberta Slip GA6-A cone 6 base glaze slow cooled

GA6-A Alberta Slip base glaze (80 Alberta Slip:20 Frit 3134) fired with Plainsman slow cool cone 6 firing schedule on Plainsman M390 iron red clay. If this is cooled at normal speed, it fires to a glossy clear amber glass with no crystals.

Ravenscrag Cone 6 Floating Blue on porcelain and a red stoneware

The insides are GA6-A Alberta Slip cone 6 base. Outsides are Ravenscrag Floating Blue GR6-M. The firing was soaked at cone 6, dropped 100F, soaked again for half and hour then cooled at 108F/hr until 1400F. The speckles on the porcelain blue glaze are due to agglomerated cobalt oxide (done by mixing cobalt with a little bentonite, drying and pulverizing it into approx 20 mesh size and then adding that to the glaze slurry).

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, but crystallizes to a stunning silky matte when fired using the schedule needed for the rutile blue (cool 100F and soak, slow cool to 1400F).

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 it this glaze on the white slip until midway down, then on the bare buff clay. These mugs are fired using a drop-and-soak firing schedule.

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 3249 (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.

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

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

Alberta Slip GA6-A clear glaze on two red bodies

GA6-A Alberta Slip base inside two red clays. The mug on left has 0.5% added tin oxide (which improves homogeneity of color, likely because it impedes crystal growth).

Low expansion version of cone 6 Alberta Slip amber glaze glaze

Alberta Slip with 20% added frit 3134 (left) fired to cone 6 on a porcelain. This is the standard GA6-A recipe. On the right 20% frit 3249 has been used instead. That is a low expansion frit so if you have crazing with the standard recipe, consider trying this one.

GA6-A Alberta Slip base glaze on a porcelain at cone 6

This is (80:20 Alberta Slip:Frit 3134). It produces an attractive transparent amber effect with excellent variation in tone with the varying thickness that occur on sharp contours.

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.

GA6-A Alberta Slip base on the insides of two bowls

This has produced a defect free fired surface at cone 6 oxidation on a dark and light burning clay body. To get this type of surface for stoneware bodies it is important to soak the kiln at cone 6, then cool it 100 degrees F and soak it again for half an hour. For coarser clays it is also helpful to program a 200 degree per hour cool all the way down to 1500F.

 


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 Calcined33.00
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. Should be ball milled.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

Ravenscrag Black on Plainsman M340

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

 


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 Calcined40.00
Alberta Slip40.00
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.

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.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

 


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 Calcined40.00
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.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

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.

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.

Speckled GA6-D glaze at cone 6.

 


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 Calcined35.00
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.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

GA6-G Alberta Slip lithium brown on the outside of a porcelain mug at cone 6. This is a thin application showing the amazing range of tones it gives.

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.

A variation of Albany lithium brown glaze. Alberta Slip 75, lithium carbonate 10, tin oxide 4, nepheline syenite 11, calcined alumina 5.

10% lithium and 4% tin do this to an otherwise transparent dull brown Alberta Slip.

Alberta Slip in the common 11% lithium and 4% tin Albany slip cone 6 glaze.

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.

Carbonate gassing can cause glaze blisters

An example of how a carbonate can cause blistering. Carbonates produce gases during decomposition. This glaze (G2415B) contains 10% lithium carbonate, which likely pushes the initial melting temperature down toward the most active decomposition temperatures.

This 1 inch tall mug is glazed with Alberta Slip plus lithium, tin and some frit.

The 85% Albany, 11% lithium, 4% tin oxide brown recipe using Alberta Slip (left) and reduced lithium content (G2415E).

G2415E Alberta lithium brown alternative recipe (cone 6)

 


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 Calcined35.00
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.

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.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

 


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 Calcined40.00
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).

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).

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.

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, but crystallizes to a stunning silky matte when fired using the schedule needed for the rutile blue (cool 100F and soak, slow cool to 1400F).

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).

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.

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

Alberta Slip Floating Blue (left) plus 4% spodumene (right).

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% Ravenscrag Slip and 20% frit 3134). This glaze requires slower cooling. It looks the best on dark bodies.

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).

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).

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!

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.

The rutile mechanism in glazes

2,3,4,5% rutile added to a 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.

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.

 

Courtesy of Digitalfire Reference Library

Alberta Slip Cone 5 Reduction Base Glaze

Code: GA6-A

The same 80:20 Alberta Slip:Frit base recipe that works at cone 6 oxidation also works in reduction

Alberta Slip Calcined40.00
Alberta Slip40.00
Frit 313420.00
100.00

GA6-A at cone 5R on Plainsman M370, M350

GA6-A is Alberta Slip raw:calcine mix with 20% frit 3134.

Ravenscrag Slip GR6-A (20% frit 3134) and Alberta Slip GA6-A (20% frit 3134) glazes on M340 at cone 5 reduction.

GA6A glaze fired at cone 5R on Plainsman M350 and M340.

GA6A glaze (Alberta Slip 80%, Frit 3134 20%) at cone 5R (left) and pure Alberta Slip at cone 10R (right).

Calcining Alberta Slip

Calcined Alberta Slip (right) and raw powder (left). These are just 5 inch cast bowls, I fire them to cone 020 and hold it for 30 minutes. Why calcine? Because for glazes having 50% or more Alberta Slip, cracking on drying can occur, especially if it is applied thick (Alberta Slip is a clay, it shrinks). I mix 50:50 raw:calcine for use in recipes. However, Alberta Slip has an LOI of 9%, so I need to use 9% less of the calcine powder (just multiply the amount by 0.91). Suppose, I needed 1000 grams: I would use 500 raw and 500*.91=455.

 

Alberta Slip is a product of Plainsman Clays and is mined in North America's premier "Clay Country" (near Ravenscrag, Saskatchewan, Canada and also in Montana, USA)