Modification Date: 2016-09-11 21:21:50
Member of Group: AS10
By adding a little iron to 100% Alberta Slip you can make an iron crystal glaze.
|Alberta Slip Calcined||50.0||48.5%|
|Red Iron Oxide||3.0||2.9%|
|Rate (C)||Temp (C)||Hold (Min)||Step|
Typically this type of glaze is made by adding up to 15% iron oxide to a transparent glaze. However using Alberta Slip, you only need 3% iron (this is an advantage because 10% iron flocculates the glaze, requiring the addition of more water which in turn causes crawling). Adjust the iron to get the amount of crystal development and metallic appearance desired. In reduction the extra iron will flux it more so melting should be good.
This is fired in cone 10R. The effect becomes more intense by 5%. To achieve this same effect using Ravenscrag, which has much less natural iron content, 10% added iron is needed (which is, of course, much messier to work with).
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.
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