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allenc27

How to make oxide mix use as under glaze

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Hi, 

I plan to brush iron oxide as under clear glaze or over white glaze. How much amount of water do I mix them with and do I need to add slip with it? I'm totally new at this, how exactly do I mix it

 

Thanks in advance

Edited by allenc27

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Hi Allen,

From your title it sounds like you are asking about an underglaze but it could be an iron wash you are asking about, not sure.

Are you just looking to brush iron oxide under or over a glaze? If this is the case then an iron wash might be what you are looking for. A wash is put on much thinner than the typical underglaze or slip. One cone 6 -10 iron wash recipe is 25 ball clay, 25 nepheline syenite, 50 red iron oxide, mixed with water to a thin consistency. I would try it on a test tile under your glaze before using it on a real pot. If your glaze is high in calcium it will bleach out the iron and it will turn a straw colour. Like everything in ceramics test it first.

Underglazes are formulated to go on greenware or bisque, usually have a frit base so they don't shrink excessively which would in turn cause cracking and lifting issues. There are commercial brown underglazes available, you can make them yourself but it's not cost effective. Underglazes can also be used overtop of glazes but with some colours there could be food safety issues with not having a covering glaze over them. Underglazes are typically made with stains not raw oxides.

If you use slip with iron oxide there will be shrinkage and cracking issues if you put it on a bisque fired pot under or over the glaze. Slips are typically put on the pot as soon after making the pot as possible so the slip and the pot shrink together. Stains, opacifiers, colouring oxides and carbonates can be added to slips. If you are using a white or light coloured clay then using the same claybody to make the slip is ideal as the pot and slip will have the same shrinkage rate.

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