|Monthly Tech-Tip |
Modified: 2020-12-01 19:51:14
Plainsman Cone 6 Alberta Slip based glaze. It can be found among others at http://albertaslip.com.
|Alberta Slip 1000F Roasted||35.00||36.5|
|Ferro Frit 3249||17.00||17.7|
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.
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.
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.
Alberta Slip Glaze Recipes
Alberta Slip is a substitute for Albany Slip that has gained a life of its own so that there are now many glazes based specifically on it.
Plainsman Cone 6 Electric Standard
Used in the Plainsman lab to fire clay test bars in our small kilns
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.
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|By Tony Hansen|
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