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Low Fire Glaze On Porcelain


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#1 kennedy james

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Posted 09 March 2014 - 03:07 PM

is it food safe to use a low fire glaze (05) on a porcelain piece bisqued at 04 ?



#2 Tyler Miller

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Posted 09 March 2014 - 03:15 PM

Maybe.  There are a lot of variables.  For instance, a lot of low fire glazes aren't food safe to begin with. Then, there's the question of glaze fit.  One thing that is certain is that you're not going to get the most out of your porcelain.  It won't be as durable as it would be when fully vitrified.

 

What are you trying to do? 



#3 Chris Campbell

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Posted 09 March 2014 - 04:13 PM

I agree with Tyler ... Porcelain is weak at 04-05 .... Why use porcelain when you could use a low firing white clay?

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#4 JBaymore

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Posted 09 March 2014 - 05:06 PM

Even if you solve the "food safe" question (see the FAQ file in the Technical section for more on that stuff).... you'll have a piece of functional ware that is not at ALL durable. Look at it cross-eyed and it''ll break.

 

Why the question?

 

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#5 kennedy james

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Posted 10 March 2014 - 01:06 PM

ok I see, not worth it then

 

I just really like a low fire glaze I've found (food safe) and don't seem to be able to find something similar in high fire glazes

 

it's the Amaco Opalescent Black Tulip

http://www.dickblick...lescent-glazes/

 

I could try to fire it at cone 5/6 and see how it looks but then I wonder if it will still be food safe...



#6 Benzine

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Posted 10 March 2014 - 03:46 PM

ok I see, not worth it then

I just really like a low fire glaze I've found (food safe) and don't seem to be able to find something similar in high fire glazes

it's the Amaco Opalescent Black Tulip
http://www.dickblick...lescent-glazes/

I could try to fire it at cone 5/6 and see how it looks but then I wonder if it will still be food safe...

If you change the firing conditions of a commercial glaze, that is labeled food safe, there is no guarantee it will still be as such, nor would they stand behind it.

I use Amaco glazes, in my classroom, and am quite happy with them. They claim their glazes have a good fit, with the low fire wares, which I can attest to. However, I would imagine the glaze won't fit well at all, with a high fire clay, that it wasn't intended for. I would also imagine, at a higher temp, it will run everywhere, and not develope the same look.

If you REALLY wanted to use that glaze, and not find a high fire alternative, you could fire the porcelain to it's full temperature, bare, then glaze and fire low, to mature the glaze. Glazing vitrified wares is a bit of a pain though, but possible.
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#7 Tyler Miller

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Posted 10 March 2014 - 04:30 PM

I'm not 100% convinced that glaze is food safe.  It's warranted to be lead and cadmium free, which is the only thing that legally matters, but it gets a "CL" caution label (refer to the MSDS on the link you posted) because it contains 5% copper.  I've never had a copper glaze that didn't want to leach copper.  Copper isn't the most toxic thing in the world, but it makes things taste like metal and people can be severely allergic to it.

 

Are you friends with any ceramicists in your area?  Sometimes having someone there, in person, to bounce ideas off of and explain what you're looking for can be really helpful.  I dunno, just a suggestion.



#8 JBaymore

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Posted 10 March 2014 - 05:55 PM

 

If you change the firing conditions of a commercial glaze, that is labeled food safe, there is no guarantee it will still be as such, nor would they stand behind it.

 

A very important point to understand in all this is that the manufacturers of ANY glaze DO NOT in any way indemnify the end user of their products for any damages or harm that comes thru the use of their products.  They NEVER "stand behind it". 

 

YOU are the one to make decisions about the materials selected for use in the manufacturering of your products. 

 

You and only you (unless you are some sort of partnership) are responsible for any damages caused by YOUR products to anyone.

 

If later you want to try to go after the manufacturer of the glaze or clay to get restitution from them ....... that is a legally separate matter.  Know that you'll be fighting a large company with a bevy of lawyers.  And look at the disclaimers they have everywhere (which you should be reading) ........ you'll lose.

 

best,

 

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


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

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#9 JBaymore

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Posted 10 March 2014 - 05:57 PM

I'm not 100% convinced that glaze is food safe.

 

Ditto.

 

best,

 

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


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

http://www.JohnBaymore.com

#10 kennedy james

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Posted 10 March 2014 - 06:55 PM

thanks everyone for the replies! you've been very helpful!

 

I'm not going to use this glaze then, because I really don't want to take the risk to have copper leaching






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