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Enamel versus glass on pottery


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#1 docweathers

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Posted 09 December 2012 - 06:16 PM

How come you can put glass on steel in the form of enamel and it doesn't crack whereas if you put glass on pottery it cracks? I would think the expansion rates of glass and pottery are more similar than glass and steel. How could you put glass on pottery to get it to melt like enamel on steel versus cracking? There must be something special about the way the enamel glass is compounded since I have played with welding glass to steel with my TIG welder and you don't get anything that looks like enamel.

Larry

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#2 Mark C.

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Posted 09 December 2012 - 08:51 PM

DocW
Glaze is glass and it does work on pottery at many different temps depending on how its formulated.
Enamel is very low temperature heavily fritted glass if I recall
Glass like bottles melt and slump at very low temps
Many low fire glazes are fritted recipes
Not sure if this info answers your thoughts.
mark
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#3 weeble

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Posted 10 December 2012 - 02:38 AM

Check the temperatures, if I recall correctly back a million years ago in grade school we enameled on copper. The copper didn't melt, but the special powders we used did, making some very nice doodads for Christmas presents one year. Nowadays, I have occasionally been known to drop bits of copper wire on a glazed surface for some very cool effects, but there the copper certainly melts, usually somewhere around my bisque temperatures. So the two processes are not as comparable as you might think, but both involve some carefully planned glass formulations.
Maryjane Carlson

Whistling Fish Pottery

#4 TJR

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Posted 10 December 2012 - 10:26 AM

Check the temperatures, if I recall correctly back a million years ago in grade school we enameled on copper. The copper didn't melt, but the special powders we used did, making some very nice doodads for Christmas presents one year. Nowadays, I have occasionally been known to drop bits of copper wire on a glazed surface for some very cool effects, but there the copper certainly melts, usually somewhere around my bisque temperatures. So the two processes are not as comparable as you might think, but both involve some carefully planned glass formulations.


Weebie;
Back in the day, every art room had a little enamel kiln that was used for copper enamelling. These were about a foot square and could be plugged in to a 110 household outlet. It was discovered that the enamel was lead based and hugely dangerous with noxious fumes pouring out. Of course nothing was vented in those days. The program was scrapped.
You could still by those little kilns-great for test kilns, they had a kiln sitter and everything, but the program was toast.
TJR

#5 docweathers

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Posted 10 December 2012 - 12:43 PM

I got the theory now . What kind of fluxes etc. would I add to ordinary wine bottle type glass to keep it clear and make it flow on pottery like enamel does on steel?

Larry

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#6 bciskepottery

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Posted 10 December 2012 - 06:15 PM

Re: "Back in the day, every art room had a little enamel kiln that was used for copper enamelling. These were about a foot square and could be plugged in to a 110 household outlet. It was discovered that the enamel was lead based and hugely dangerous with noxious fumes pouring out. Of course nothing was vented in those days. The program was scrapped.
You could still by those little kilns-great for test kilns, they had a kiln sitter and everything, but the program was toast."

You don't want to buy a kiln that previously was used with lead glazes . . . it is contaminated. When buying an old used kiln, it is best to check for lead before buying.

#7 Mark C.

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Posted 10 December 2012 - 07:04 PM

I got the theory now . What kind of fluxes etc. would I add to ordinary wine bottle type glass to keep it clear and make it flow on pottery like enamel does on steel?


Yours is a very general statement/question
Your bottles will flow onto a flat contained clay surface I'm guessing at 1300-1500 F no materials needed to add .You are going to have to test this to find out . I doubt it common knowledge as its outside most who deal with clay-I only know about glass bottles slumping because back in the day(70s) I made my own beer and wanted to fire in some homemade labels on longneck beer bottles and they slumped before luster temps.About dull red heat.
Good luck on this experiment let us know how it turns out.
Mark
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#8 docweathers

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Posted 10 December 2012 - 10:48 PM

My four dollar blender works great for glazes.

What causes the cracking that one normally sees with glass on ceramic, and how do you avoid that?

Larry

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#9 Mark C.

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Posted 10 December 2012 - 11:20 PM

I think you must be talking about crazing-which can be a good if its under the glaze surface and not thru it. This can be from a glaze that does not FIT the body well
This has been covered a bunch here and can be searched
You can adjust the glaze or try another clay body.
Most of my glazes do not craze-the reds can if applied to thick
I make my own and fire cone 10- 11.
If its commercial glaze I'm no help as you will not have a formula.
Mark
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#10 docweathers

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Posted 10 December 2012 - 11:33 PM

I'm still perseverating on glass (not glaze) and how to get it to run smoothly versus the cracking that is most common.

I mix my own glazes too, which makes the something of the mad chemist or alchemist.

Larry

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#11 TJR

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Posted 11 December 2012 - 10:26 AM

Re: "Back in the day, every art room had a little enamel kiln that was used for copper enamelling. These were about a foot square and could be plugged in to a 110 household outlet. It was discovered that the enamel was lead based and hugely dangerous with noxious fumes pouring out. Of course nothing was vented in those days. The program was scrapped.
You could still by those little kilns-great for test kilns, they had a kiln sitter and everything, but the program was toast."

You don't want to buy a kiln that previously was used with lead glazes . . . it is contaminated. When buying an old used kiln, it is best to check for lead before buying.


bciskepottery;
I think I was misunderstood here. I was trying to explain the dangers of copper enamelling and why it is no longer used in schools. I had two of those little kilns that I got from out school board surplus warehouse for free. I did not end up using them as the wiring was not working. I guess you have a point about not using something that had lead in it[as in copper enamelling], but I was trying to say the same thing-that lead fumes are dangerous. I apologize if you misunderstood.
TJR.

#12 weeble

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Posted 13 December 2012 - 03:59 AM

Doc, the problem is bottle glass is a mishmash of chemicals. Glaze is a mishmosh of chemicals. Without knowing exactly what the MISHMASH is, its hard to say what to mix into it to make a MISHMOSH. And to make it even MORE problematic, different bottles have different mixes in the mishmash.

There is no one answer. All you can do is test test test.
Maryjane Carlson

Whistling Fish Pottery




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