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Low Fire Glaze on High Fire Clay?


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#1 podgen

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Posted 02 September 2011 - 06:51 PM

Let's say I want to make something with high fire clay that needs to be fired to cone 10 for vitrification.
Let's say I also want to use some premixed low fire glazes such as are used in schools on cone 05-06 earthenware.

What would happen if I fire the piece to cone 10, then paint it with the low fire glazes, then fire to the low fire temperature.

Will this work out okay or will the clay and glaze be incompatible in some way? Does it matter that the clay body will not be as open and porous when painted as it would be if it were just bisqued normally?

#2 Dinah

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Posted 03 September 2011 - 04:36 PM

The way most folks do this is to bisque to ^04 or ^05 then gloss fire up to the ^10 with the appropriate glazes. I'm worried also -- in thinking about it -- that your glaze take up on a highly vitrified body will be poor and require heat gun on the pots to dry the glaze coats (sprayed usually) based my experience of reglazing pieces which have been gloss fired to ^8/9. If you're stuck with ^10 body and a supply of low temp glazes well go for it, but it is not a particularly cost effective practice. Is there anyone around who you can swap the clay body out with to get a ^04 -^6 body?
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#3 clayshapes

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Posted 04 September 2011 - 10:44 AM

I've done something like this before -- it works but is not perfect.
I created pieces with stoneware (cone 6) clay, bisque fired it in the usual way (to 04) and then used low fire earthenware glazes and fired again to 04. The clay obviously isn't vitrified - but I liked the colors - so that's why I did it this way.
If you fire to cone 10 and then apply glaze (any glaze) it will adhere, but won't be great. Try it though -- warm the pot first before applying the glaze.
I used to do what you are suggesting because I liked the low fire glazes better -- I was doing bright colors. However, I've found lots of good mid fire glazes (cone 6, that is) that are the same, and better, than the low fire glazes. And of course there is a huge advantage in the clay being vitrified. There are lots of commercial mid fire glazes in great colors -- take a look at Amaco and Laguna and Speedball.
As for cone 10 glazes...I have no experience. Are you using porcelain?

#4 Chris Campbell

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Posted 04 September 2011 - 11:25 AM

Porcelain artists do this all the time ... Fire high first then glaze fire low. On functional pieces they would have a high fire glaze on the eating surface during the high fire, then the low fire glaze on the outside or bottom for the low firing. They do this because porcelain slumps so needs to be well supported during high temps.

The glaze will not want to stick to a vitrified piece so you can pre heat the pottery in an oven. Some people add cmc gum to the glaze to make it adhere.

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#5 podgen

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Posted 05 September 2011 - 07:50 PM

If you fire to cone 10 and then apply glaze (any glaze) it will adhere, but won't be great. Try it though -- warm the pot first before applying the glaze.
I used to do what you are suggesting because I liked the low fire glazes better -- I was doing bright colors. However, I've found lots of good mid fire glazes (cone 6, that is) that are the same, and better, than the low fire glazes. And of course there is a huge advantage in the clay being vitrified. There are lots of commercial mid fire glazes in great colors -- take a look at Amaco and Laguna and Speedball.
As for cone 10 glazes...I have no experience. Are you using porcelain?

Yeah I think mid fire is a good option. I'm doing all cone 10 right now but also have access to low fire glazes somewhere else. Some porcelain, some stoneware.

Porcelain artists do this all the time ... Fire high first then glaze fire low. On functional pieces they would have a high fire glaze on the eating surface during the high fire, then the low fire glaze on the outside or bottom for the low firing. They do this because porcelain slumps so needs to be well supported during high temps.

The glaze will not want to stick to a vitrified piece so you can pre heat the pottery in an oven. Some people add cmc gum to the glaze to make it adhere.

Neat, thanks for the info. I will definitely glaze the inside at least first if I do this.
The low fire glaze would be coming out of those jars. Do you have any idea whether painting cmc gum over the area to be low fire glazed would work? Or would some amount of glaze have to be removed from the jar, cmc gum added, then discard what is not used? Or just dump it back into the jar?

#6 scoobydoozie

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Posted 06 September 2011 - 07:30 AM

Try adding Apt II to the amount of glaze you need to cover the piece to help it adhere. I use it to help unfired glaze stick to fired glaze when I have to refire a touch up. Works great!






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