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#1 Iforgot

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Posted 27 November 2012 - 10:46 PM

Hey world,

I have a test tile in the studio that is lithium carbonate mixed with just enough water to make a thick paste which was applied to bisque and fired to ^5 oxidation, this made a beautiful eggshell color. Do you think this would be food safe as a glaze?


Darrel
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#2 Mark C.

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Posted 27 November 2012 - 11:17 PM

It still will have water soluble effects so I would say no.
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#3 JBaymore

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Posted 27 November 2012 - 11:21 PM

It'd be quite unstable. A small amount of lithium carbonate contains a HUGE number of Mols of lithium atoms due to the molecular weight. The only place thjey are getting something to bind them is by "stealing" (fluxing) some silica from the clay body. So the glass showing on the surface is a pretty oversupplied one with lithium oxide.

best,

...............john
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#4 yedrow

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Posted 28 November 2012 - 01:04 PM

Is that true for all glazes using lithium carb.? I know lithium tends to go into solution in the glaze [er, slurry], is that also true for the melt? I've just assumed it increased pinholing/blistering.

Joel.

#5 JBaymore

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Posted 29 November 2012 - 11:03 AM

Is that true for all glazes using lithium carb.?



Joel,

No.... it is all about the relationships of the number of molecues of one oxide in the melt to the number of other oxide molecules in the melt.

BTW..........All (most of the time) of the raw materials that we use to mix up a recipe in the bucket of raw galze slurry are changed to the oxide form by the application of heat energy in the kiln. It is those oxides that become the glaze melt, and reflect the final chemical formula for the glaze. For example, lithium carbonate ( LiCO3 ) will lose carbon dioxide ( CO2 ) to become lithium oxide ( Li2O ). (That is not the exact equation there....just the concept.)

best,

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

John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#6 yedrow

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Posted 29 November 2012 - 09:59 PM

Thank's John! I reread your original post and understand it better now.

Joel.

#7 Roberta12

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Posted 04 December 2012 - 04:55 PM

John, in regards to what you said about Lithium carb when it is fired, does that make it food safe??

#8 JBaymore

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Posted 04 December 2012 - 05:07 PM

John, in regards to what you said about Lithium carb when it is fired, does that make it food safe??


No.

There are many things that people do in ceramics studios that are evaluated purely by what could be called the "Mark I Eyeball" test. What that means is if the thing looks good to the eye... then it is put in use. This is a shallow and misleading approach. It is fine if you are not concerned about things like food safety or potential archival quality (deterioration/changes to the surface over time).

Washes of things like copper carbonate or copper chloride, cobalt carbonate or cobalt chloride, lithium carbonate, gerstly's borate, and son on are among the many, many that are used without much regard to what exactly you are putting on there.

It is an unfortunate fact of life that ceramics has a heavy technical side.

best,

.......................john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

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#9 perkolator

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Posted 04 December 2012 - 05:07 PM

essentially...NO, it does not make it food safe. "food safe" depends on many factors and proper testing would be necessary to determine. most likely, it's not going to be food safe according to today's standards.

are you mostly interested in the eggshell COLOR or the eggshell SURFACE? either way, there are many ways to achieve either - and they can be food safe too.

#10 Roberta12

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Posted 04 December 2012 - 06:55 PM


John, in regards to what you said about Lithium carb when it is fired, does that make it food safe??


No.

There are many things that people do in ceramics studios that are evaluated purely by what could be called the "Mark I Eyeball" test. What that means is if the thing looks good to the eye... then it is put in use. This is a shallow and misleading approach. It is fine if you are not concerned about things like food safety or potential archival quality (deterioration/changes to the surface over time).

Washes of things like copper carbonate or copper chloride, cobalt carbonate or cobalt chloride, lithium carbonate, gerstly's borate, and son on are among the many, many that are used without much regard to what exactly you are putting on there.

It is an unfortunate fact of life that ceramics has a heavy technical side.

best,

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




Thanks for the info.....I should have been more clear with my question, also. I was talking about the Lithium carb changing to Lithium oxide when it's fired, when it is in a glaze. So.....what I am getting out of this post is.....test test test....and become educated enough about what you are using, so as not to inflict harm on your customers. The reason I turned to this particular forum, is that a customer told me when she put her cranberry sauce in a bowl she bought from me, it changed the color of the bowl. The glaze is/was my new favorite, fall creek shino (green) (I was suitably horrified!) So, I was thinking about the lithium that is in the glaze, as well as the copper carb. I appreciate the knowledge a person can gain from this forum......so, I guess I should send off a sample of this glaze?? discontinue using it?? use it for non food use only??

#11 JBaymore

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Posted 04 December 2012 - 11:13 PM

The reason I turned to this particular forum, is that a customer told me when she put her cranberry sauce in a bowl she bought from me, it changed the color of the bowl. The glaze is/was my new favorite, fall creek shino (green) (I was suitably horrified!) So, I was thinking about the lithium that is in the glaze, as well as the copper carb. I appreciate the knowledge a person can gain from this forum......so, I guess I should send off a sample of this glaze?? discontinue using it?? use it for non food use only??




Don;t bother wasting your money. If there is a color change.... it would fail anyway.

Non food use only.

Shinos are typically not all that stable. BUT...and this is an IMPORTANT "but"...... the traditional ones (non spodumene based) do not contain any particularly harmful constituients. So even if they hleach... they do not leach anything bad. However if you start sticking colorants in them...... THAT changes the situatioon, depending on the toxicity of the colorant and how much leaches.

best,

......................john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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