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GA6-F - Alberta Slip Cone 6 Oatmeal

Modified: 2022-04-12 10:30:34

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

Notes

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.

Related Information

Rutile in functional glazes:

Push the limit and you might get this

This picture has its own page with more detail, click here to see it.

The 80:20 GA6-A Alberta Slip base becomes oatmeal-like when oversaturated with rutile and/or titanium (left: 6% rutile + 3% titanium dioxide; right: 4% rutile + 2% titanium dioxide). The rough surface results from excessive crystallization of titanium-bearing phases from the melt during cooling. It is unpleasant to touch, readily shows cutlery marking and is less desirable for functional surfaces. In glazes of this type, rutile additions above about 4% can become increasingly difficult to keep smooth and consistent. Crystallization, rather than phase separation, increasingly dominates the variegation mechanism.

One way of avoiding problems is staying below the tipping point, 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 and kiln cooling). Surprisingly, making the glaze more fluid does not necessarily solve the problem. Greater melt fluidity increases ion mobility and can actually promote crystal growth during cooling, producing an even rougher surface.

Cone 6 black with a second layer of oatmeal glaze

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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 roasted Alberta or Ravenscrag Slips to establish a balance between drying hardness but not too much drying shrinkage (and resultant cracking).

Roasting Alberta and Ravenscrag Slips at 1000F: Essential for good glazes

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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.

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