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Alberta Slip Calcined

Alternate Names: Calcined Alberta Slip

OxideAnalysisFormula
CaO6.62%0.382
MgO4.37%0.351
K2O3.93%0.135
Na2O2.47%0.129
P2O50.11%0.003
TiO20.34%0.014
Al2O317.05%0.541
SiO260.06%3.236
Fe2O35.05%0.102
Oxide Weight323.86
Formula Weight323.86
If this formula is not unified correctly please contact us.

The chemistry of this material is slightly different than for raw Alberta Slip (it does not lose any weight on firing, so it supplies more of each of the oxides to the fired glaze, almost 10% more). The chemistry provided here assumes complete calcination (to at least cone 04). However there is an issue. The page at albertaslip.com recommends calcining to only 1000F, at that temperature it looses only 3% weight on firing (so this chemistry is not correct).


Calcining Alberta Slip

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.

Why does the glaze on the right crawl?

Why does the glaze on the right crawl?

This is G2415J Alberta Slip glaze on porcelain at cone 6. Why did the one on the right crawl? Left: thinnest application. Middle: thicker. Right thicker yet and crawling. All of these use a 50:50 calcine:raw mix of Alberta Slip in the recipe. While that appears fine for the two on the left, more calcine is needed to reduce shrinkage for the glaze on the right (perhaps 60:40 calcine:raw). This is a good demonstration of the need to adjust raw clay content for any glaze that tends to crack on drying. Albertaslip.com and Ravenscrag.com both have pages about how to calcine and calculate how much to use to tune the recipe to be perfect.

Something is definitely wrong. What is it?

Something is definitely wrong. What is it?

An example of how a glaze that contains too much plastic clay has been applied too thick. It shrinks and cracks during drying and is guaranteed to crawl. This is raw Alberta Slip. To solve this problem you need to tune a mix of raw and calcine material. Enough raw is needed to suspend the slurry and dry it to a hard surface, but enough calcine is needed to keep the shrinkage low enough that this cracking does not happen. The Alberta Slip website has a page about how to do the calcining.

Will this crawl when fired? For sure!

Will this crawl when fired? For sure!

This high-Alberta-Slip glaze is shrinking too much on drying. Thus it is going to crawl during firing. This common issue happens because there is too much plastic clay in the glaze recipe (common with slip glazes). Clay is needed to suspend the other particles, but too much causes the excessive shrinkage. The easiest way to fix this is to use a mix of raw and calcined Alberta Slip (explained at albertaslip.com). The calcined Alberta Slip has no plasticity and thus much less shrinkage (but it still has the same chemistry). Many matte glazes have high kaolin contents and recipes will often contain both raw and calcined kaolin for the same reason.

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By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Alberta Slip Calcined" descrip="" searchkey="Calcined Alberta Slip" loi="0.00" casnumber=""> <oxides> <oxide symbol="CaO" name="Calcium Oxide, Calcia" status="" percent="6.620" tolerance=""/> <oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="" percent="4.370" tolerance=""/> <oxide symbol="K2O" name="Potassium Oxide" status="" percent="3.930" tolerance=""/> <oxide symbol="Na2O" name="Sodium Oxide, Soda" status="" percent="2.470" tolerance=""/> <oxide symbol="P2O5" name="Phosphorus Pentoxide" status="" percent="0.110" tolerance=""/> <oxide symbol="TiO2" name="Titanium Dioxide, Titania" status="" percent="0.340" tolerance=""/> <oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="17.050" tolerance=""/> <oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="60.060" tolerance=""/> <oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="5.050" tolerance=""/> </oxides> </material>


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