Food Safe? Oxides On Glazes

[preeta]

If i use oxides on top of a food safe glaze would the end result still be food safe?

 

in our school studio, when you use RIO, rutile, cupper or manganese under clear or any translucent glaze they mostly disappear. that is why i am thinking of oxides on top of a satin white glaze.  

 

 

[bciskepottery]

The only way to make certain is to have the wares tested. The taste of acidic foods -- oranges, lemons, tomatoes -- can be affected by copper if it leaches. The oxides may discolor, also, if not fully covered and sealed. It will also depend on whether your satin white glaze is fully melting or achieves its look by being under-fired.

[Marcia Selsor]

I think it is better to use an under glaze.

But, yes, you need to test.

Marcia

[preeta]

thank you both for your prompt answer. i was thinking if one can use a cast iron pan to cook in why cant i use at least RIO on glazes. 

 

can i tell by eye if something is underfired? or will the heat tell me. 

 

the satin white behaved differently in reduction when the temperature goes to ^6 or ^6 1/2 as opposed to oxidation. 

 

i will do the lemon and vinegar test. 

[High Bridge Pottery]

You could try mixing the raw oxides with clay to make a coloured slip which will probably stay put and not dissolve into the glaze as much.

 

Can't remember what percentages I used but her are a few pictures of the work I have done with coloured slips painted onto the clay before it is leather hard and then bisqued, glaze applied.

 

  

[neilestrick]

In general, if you use raw oxides on top of a glaze the oxide will be too highly concentrated. There are overglazes that can be used that way, but working under the glaze is generally easier. Commercial underglazes are great. If you are making colored slips, you'll need a pretty good amount of iron to get it to show. I use 20% iron in my slip for cone 6. Half that much for reduction. For cobalt I use 2%. They also have to go on thick enough, 2 to 3 coats, or they won't show very well.

[Mark C.]

I tend to put all my colorant glazes under my other glazes as a rule.As a cone reduction potter I like the effects as well as it incases them in the top glaze a bit.I also get better running of colors this way.The last reason is that they tend to flak off on top of glazes when dry.