Modification Date: 2018-08-14 11:44:15
Member of Group: AS6
An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares.
|Alberta Slip 1000F Roasted||40.0|
|Ferro Frit 3134||20.0|
|Rate (F)||Temp (F)||Hold (Min)||Step|
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. 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.
In our lab we can make one Canadian gallon using a mix of 2700 water and 3000 powdered glaze mix (1200 Alberta Slip, 1200 Calcined Alberta Slip, 600 Frit). This produces a specific gravity of 1.45 at about the right viscosity (and thixotropy) 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 for us. While you certainly can mix to a higher specific gravity (thus using less water), be careful as this will often make it go on too thick (and cracking will likely occur).
Do not go higher that the above-recommended specific gravity or it is likely the glaze will go on too thick. Dip ware quickly as well (to avoid it going on too thick).
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 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.
The first is on GA6-A, the rest are on GA6-C (Alberta slip glazes). The last has been applied too thickly, the brown band is dry and blistered.
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.
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.
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.
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).
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.
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!
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. 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).
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.
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.
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).
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).
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.
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.
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.
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.
This is the standard Plainsman L3954D white engobe recipe with the 10% Zircopax switched for Burnt Umber. The result is a dark, rich, ultra-gloss brown (almost black). The engobe is applied inside and half-way down the outside. The mug on the left is glazed inside and out with the base GA6A Alberta Slip cone 6 recipe (but uses Ferro Frit 3195 instead of 3134). The one on the right has the same glaze on the outside but the G2926B clear transparent on the inside (it is micro-bubbling). This engobe works even better with a black stain.
Out Bound Links
Pure Alberta Slip can be made into a black adding only 20% frit and 3% black stain
2003-12-12 - 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, in...
In Bound Links
This Plainsman Cone 6 Ravenscrag Slip base is just the pure material with 20% added frit to make it melt to a glossy natural clear.
2003-07-21 - This is the base cone 6 Ravenscrag recipe, it fires as a transparent glossy. It has an addition of the most common North American borate frit, enough ...
Archie Bray Slip
It is better to understand and have control of one good base glaze than be at the mercy of dozens of imported recipes that do not work. There is a lot more to being a good glaze than fired appearance.
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By Tony Hansen