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PotsbyChar

Food Safe Cone 05 Glaze Recipe

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I am working with a cone 05 clay body this summer and now I am looking for a good recipe for a food safe, cone 05 clear glaze. If anyone has one they would be willing to share I would be very appreciative. Thank you all in advance.

 

Charlotte

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I am working with a cone 05 clay body this summer and now I am looking for a good recipe for a food safe, cone 05 clear glaze. If anyone has one they would be willing to share I would be very appreciative. Thank you all in advance.

 

Charlotte

 

 

Well lots of people have looked at this thread but none have answered so I am assuming there are no "good recipes for food safe o5 clear glaze" out there to be had. I thank you all for reading my requests.

 

Charlotte

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The problem lies with the fact that there is no one glaze for any purpose.

It depends on your clay body matching with a glaze to give you a correct fit.

 

It's like asking what the best fitting jeans are without considering your body type.

 

You just have to test recipes with your clay and adjust as needed.

Test for food safety as you would any other dish.

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The problem lies with the fact that there is no one glaze for any purpose.

It depends on your clay body matching with a glaze to give you a correct fit.

 

It's like asking what the best fitting jeans are without considering your body type.

 

You just have to test recipes with your clay and adjust as needed.

Test for food safety as you would any other dish.

 

 

Great simile!

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Guest JBaymore

The first question here is what you actually mean by "food safe"?

 

There is no FDA nor ASTM specific standard for the term "food safe". So no one can really say a glaze is "food safe" with any kind of formal backing for the statement. The term gets tossed around a lot by potters and ceramic matrerials suppliers..... but it really has no formal "meaning" as a standard.

 

Various more local boards of health have standards for wares used in restaraunts. The US FDA regulates only the leaching of lead and cadmium from ceramic glazes; no other oxides are currently regulated. Everything you hear about barium and manganese is purely self-imposed by the ceramics commuunity.

 

For food usage, the commonly looked at characteristics of glazes are the leaching of toxic substances into foods, the fit of the glaze to the clay bnody (crazing or shivering issues), and the overall durability of the glass and clay body in food service types of situations (dishwashers, microwaves, abrasive clensers, repeated frequent washing, etc.).

 

At Orton cone 04-05 you are aleready at a bit of a disadvantage as compared to stoneware temperatures. This is because SiO2 is the "backbone" of the hard glass formers for glazes. The melting point for silica (SiO2) is quite high, so the amount of silica content that a glaze can "hold" at the lower cone end points is lower than that at high temperatures. So a lot fluxing materials are added to bring the melting point down. Also often added there is the addition of B2O3, a lower meltling glass former, but which is softer than SiO2.

 

So cone 04 glasses are typically a bit "weaker" than higher firing glazes. Working to counter this inherent trait is the "technical" issue.

 

This weaker glass matrix heads things toward issues with leaching (the bonding holding in the various chemistry components inot the glass matrix) as well as mechanical durability. And the fluxes that are active at the lower temperatures often impart a high Coeffieicnt of Reversible Thermal Expansion, which has a tendency to cause crazing at this cone range.

 

This is not to say that it isn't possible to come up with a reasonably durable and well fitting cone 04 glaze. It is just that it is a tough starting point to go at specifically for food usage. You can certainly do it yourself, but you likely will want to learn a lot about ceramic chemistry and fired product testing work to be happy with your results.

 

Likely your best bet is to go with the commercial lead free glazes; the manufacturers have teams of ceramic engineer types that have delved into this to come up with them.

 

best,

 

......................john

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The first question here is what you actually mean by "food safe"?

 

There is no FDA nor ASTM specific standard for the term "food safe". So no one can really say a glaze is "food safe" with any kind of formal backing for the statement. The term gets tossed around a lot by potters and ceramic matrerials suppliers..... but it really has no formal "meaning" as a standard.

 

Various more local boards of health have standards for wares used in restaraunts. The US FDA regulates only the leaching of lead and cadmium from ceramic glazes; no other oxides are currently regulated. Everything you hear about barium and manganese is purely self-imposed by the ceramics commuunity.

 

For food usage, the commonly looked at characteristics of glazes are the leaching of toxic substances into foods, the fit of the glaze to the clay bnody (crazing or shivering issues), and the overall durability of the glass and clay body in food service types of situations (dishwashers, microwaves, abrasive clensers, repeated frequent washing, etc.).

 

At Orton cone 04-05 you are aleready at a bit of a disadvantage as compared to stoneware temperatures. This is because SiO2 is the "backbone" of the hard glass formers for glazes. The melting point for silica (SiO2) is quite high, so the amount of silica content that a glaze can "hold" at the lower cone end points is lower than that at high temperatures. So a lot fluxing materials are added to bring the melting point down. Also often added there is the addition of B2O3, a lower meltling glass former, but which is softer than SiO2.

 

So cone 04 glasses are typically a bit "weaker" than higher firing glazes. Working to counter this inherent trait is the "technical" issue.

 

This weaker glass matrix heads things toward issues with leaching (the bonding holding in the various chemistry components inot the glass matrix) as well as mechanical durability. And the fluxes that are active at the lower temperatures often impart a high Coeffieicnt of Reversible Thermal Expansion, which has a tendency to cause crazing at this cone range.

 

This is not to say that it isn't possible to come up with a reasonably durable and well fitting cone 04 glaze. It is just that it is a tough starting point to go at specifically for food usage. You can certainly do it yourself, but you likely will want to learn a lot about ceramic chemistry and fired product testing work to be happy with your results.

 

Likely your best bet is to go with the commercial lead free glazes; the manufacturers have teams of ceramic engineer types that have delved into this to come up with them.

 

best,

 

......................john

 

 

Thanks so very much John that was very informative. I now know a lot more about what I am trying to achieve here. For the time being I will be using a commercial glaze but will be looking into mixing my own someday. Thank you again.

 

Charlotte

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