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How to make oxide mix use as under glaze


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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  • 1 year later...
12 hours ago, Mariana said:

How would iron oxide wash work on low temperature? Cone 4 for exemplo... or 1000C 
 

Try 1 part iron oxide plus 1 part frit (which ever one you usually use at low fire) plus 1 part bentonite or equal parts iron oxide plus gerstley borate. Test it and see if it's doing what you want, dilute or increase the iron or frit/gerstley borate as necessary. 

BTW, cone 4 is roughly 1160C so thinking you meant cone 04 which would be roughly 1060C.

Welcome to the forum.

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1 hour ago, Min said:
14 hours ago, Mariana said:

How would iron oxide wash work on low temperature? Cone 4 for exemplo... or 1000C 
 

Try 1 part iron oxide plus 1 part frit (which ever one you usually use at low fire) plus 1 part bentonite or equal parts iron oxide plus gerstley borate. Test it and see if it's doing what you want, dilute or increase the iron or frit/gerstley borate as necessary. 

BTW, cone 4 is roughly 1160C so thinking you meant cone 04 which would be roughly 1060C.

I use a mixture of iron oxide and water as an ink for my logo on greenware.  the bisque is fired to ~cone 07 (~950 C) and the marks are fused to the ware; therefore at 1000 C the marks will be well attached.  

Adding tiny pinch of the moist clay body can act as a carrier for the iron oxide slurry; the optimal ratio of clay body to iron oxide to water  is determined by your testing and the way you apply the marks. 

 keep it simple. 

LT
 

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