Modified: 2022-04-12 10:30:34
Plainsman Cone 6 Alberta Slip based glaze. It can be found among others at http://albertaslip.com.
|Alberta Slip 1000F Roasted
|Ferro Frit 3134
Alberta slip is well suited to oatmeal glazes because it already has the iron content needed. Vary the titanium for more or less variegation and oatmeal appearance.
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 to experiment.
An advantage of this recipe is that the oatmeal effect is achieved without the use of manganese.
This recipe was referred to as GA6-B in past.
For mixing instructions please see the master recipe, GA6-A.
The 80:20 base GA6-A Alberta slip base becomes oatmeal when over saturated with rutile or titanium (left: 6% rutile, 3% titanium; right: 4% rutile, 2% titanium). That oatmeal effect is actually the excess titanium crystallizing out of solution into the melt as the kiln cools. Although the visual effects can be interesting, the micro-crystalline surface is unpleasant to touch and susceptible to cutlery marking and leaching (not as stable or durable as in glazes which are pure amorphous glass). For functional ware, rutile glazes are among the most troublesome to keep consistent, one way of avoiding problems is keeping the percentage as low as possible while still getting the desired variegation (of course that will vary depending on the melt fluidity of the glaze, more highly fluid ones can handle more rutile or titanium).
The underglaze is G1214M cone 6 black (adds 5% Mason 6666 black stain). Overglaze left: GR6-H Ravenscrag Oatmeal. Overglaze right: GA6-F Alberta Slip oatmeal. Both produce a very pleasant silky matte texture (the right being the best). Both layers are fairly thin. In production it would be best to spray the second layer, keeping it as thin as possible. It is also necessary to adjust the ratio of raw to calcined Alberta or Ravenscrag Slips to establish a balance between drying hardness but not too much drying shrinkage (and resultant cracking).
Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about 1 kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying (if used raw the GA6-B and similar recipes will crack as they dry and then crawl during firing). Roasting eliminates that. Calcining to 1850F sinters some particles together (creating a gritty material) while roasting to 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.
GA6-A - Alberta Slip Cone 6 transparent honey glaze
An amber-colored glaze that produces a clean, micro bubble free transparent glass on brown and red burning stonewares.
GR6-H - Ravenscrag Cone 6 Oatmeal Matte
Plainsman Cone 6 Ravenscrag Slip glaze. See more at ravenscrag.com.
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|By Tony Hansen
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