Newbie (Dumb Question) Why can't one put glaze on Greenware?

You can and some potters do. It's call raw firing. There are definitely some advantages to bisqueing before glazing - it burns the nasties out of the clay before the glaze firing and it makes the pieces easier to glaze. Also, glazes intended for bisque work may not work well on pieces that haven't been bisqued. Glazes for raw firing typically have a high clay content.

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Theoretically you can, but greenware is hard to handle, very fragile, and the clay would soften as you dip it in the glaze. This is a problem especially with thin pieces. The glaze doesn't soak in, the water soaks in, leaving the glaze particles on the surface, the same as in bisqued ware. Yes, clay shrinks in drying, in bisque firing and in glazefiring. How much it shrinks altogether depends on the clay you use.

Monika

-- Monika Schleidt snipped-for-privacy@schleidt.org

Yes you can Glaze pots at the greenware stage - they can also be glazed at the bone dry stage.

For a glaze to work on greenware it has to accomodate the shrinkage that occurs as the clay dries, in practice this usually means having a glaze with ball clay in it (30% is a rough guide). The glaze then has to be re-formulated that is other ingredients adjusted so that the fired glaze has the same proportion of the various oxides (not such a daunting task witha glaze calculation program). You may find recipes for suitable glazes, probably referred to as "slip glazes".

If you then want to fire the pots in one go (once firing) the firing cycle has to be adjusted so that it starts like a biscuit firing has about an hour soak at 900 deg Celsius, and then continues like a glaze firing.

To glaze at the bone dry stage you may get away with using a glaze formulated for biscuit if it has some clay in it or add about 5% bentonite to a biscuit glaze (don't just add to the liquid glaze -either mix into dry igredients or if you have to add to an already mixed glaze mix with a small amount of the glaz and then sieve it into the glaze mix).

Dennis Parks wrote a book - can't remeber the exact title but something like "Oil firing and Raw glazing" Also Andrew Holden "The self reliant potter" published around 1980 has a section on raw glazing Iv' just rembered tha Fran Tristram has a book about Once firing publishe by A&C Black.

Have your eyes started to glaze yet??

Thanks for the info. No.. I have not yet put any glaze on greenware...

I was just thinking about it and I did not understand "why not"...

I think, I will try "slip" type first...

Thank again....

The glaze you would want to use is called under glaze. You can put this glaze on either green ware or bisked ware. But if you put the under glaze on while it's still green you would than want to put a clear coat on. My instructor showed us an example of what happens when he put a glossy glaze on a green ware pot. It ran down the side of the and left a ring at the bottom because the glazes had nothing to stick to. A.G.

"Amber" wrote in news:FxRmb.39283$ snipped-for-privacy@twister.tampabay.rr.com:

You may find this hard to believe but once upon a time all pottery was green glazed.

As far as I am aware bisquet firing is a recent western tradition and was only introduced to England in the 17th century from France as an industrial process. Even now days it is only industrial factories, studio potters and teachers of ceramics and their pupils who bisque fire.

I would imagine that the majority of readers of this group have never tried it out.

Glaze formulation for green ware is no more diffficult than formulating a well fitted glaze for low or high fired bisque. The main thing to know is the shrinkage of the clay from green to the final fired temperature. This can be done by experimentation with the clay body.

Of course you need to design products that are suitable for the process.

Cheers

John W

No underglaze is a different thing. You can glaze greenware, or unbisqued pottery at the leather hard stage (more difficult because of drying shrinkage) or at the bone dry stage. Glazes mostly have to specifically formulated for "once fired" work. It has dissadvantages, application of the glaze can be done with spraying, painting, or very carefully dipping but you run the risk of the pottery getting too wet and just falling to bits, or even falling to bits into the bucket of glaze, and thus also ruining your glaze. Bisquing also removes impurities that can cause pinwholing and other problems. Underglaze are colourants that go under a glaze, best IMO applied to dry unfired work. It is then bisqued and a clear glaze applied and fired again. If you underglaze bisqued ware you often have to refire before glazing to burn off gums etc used to make underglaze flow well, but which are inclined to resist the glaze a little. Yes John I have tired once fired work, its fun :o) A

You can put glaze on greenware. I read of a potter who never bisqued (he was firing low fire). So, I gave it a whirl. The glaze matured properly and stayed on the pots. However, the reds turned either green or went clear and the coppers turned black. I now have an off-white apple that I did for one of the testers and my Armegeden piece which was supposed to be oozing blood out of a copper body, is oozing green stuff out of a black body instead. Considering the piece, I like my accidental result better than the one I had planned.

Jan C.

What type of "glaze"?

Right now, all my stuff is packed ready to move next week. I don't remember the brand or the color designator, but I used commercially prepared low-fire glazes for this experiment. I used the same glazes on other test pieces that had been bisqued and the colors were as advertised. If you need, when I get my studio upacked (first thing, before even my kitchen gets unpacked), I'll look up the specifics and get back to you.

Jan C.

No that is fine... I just wanted to know if it was a commercial type glase... I will try it this weekend...