Using an Underglaze as a Primer?

[Ben xyz]

In an attempt to salvage,  I was thinking of covering a previously fired piece (at cone 5 / matte glaze) with a white Underglaze as a kind of primer, before glazing and firing again. Tried it? I know re-glazing a fired piece is a hit-and-miss proposition at best. There's also the possibility of bisque firing this pre-primed object before applying another glaze and firing c5.

Had also heard about heating a surface somewhat (w/ heat gun) and then spraying on a glaze for better adhesion to a previously glazed/fired piece. Any luck?

[Bill Kielb]

I have not had great results refiring to cone, nor do I think underglaze will act as a decent primer, but ya never know what the result will be till you try. To drastically change the look, I have fired down  over an existing glaze and had reasonable success with lowfire glaze though (similar to some production wares that go to cone first to weed out potential failures in advance) so maybe an idea that is worth mentioning. Heating the ware and spraying the final glaze made even application very doable.

Edited September 27, 2023 by Bill Kielb

[Callie Beller Diesel]

Remember that just because a glaze is matte once fired, that doesn’t mean it isn’t fluid in the kiln. So re-melting it with a layer of underglaze is going to melt the underglaze into the surface of the first layer, which will probably leave a bit of a half melted surface. If you throw another glaze on top of that, you’ll be creating something called a eutectic, which is a fancy way of saying the 2 glazes are going to steal materials from each other in a way that will make them melt even more actively than the 2 do separately. This effect is usually more pronounced when you combine a matte and a glossy glaze.

Could this be interesting? Maybe. Depends on the context. Could be a really interesting sculptural effect, but something that’s wildly impractical on a functional piece. Could this make a mess in the kiln? More than likely. If you try it, use a waster with a lip that can contain any runoff, and make sure the person firing the kiln is ok with you doing this. Will this fix a mug? Doubtful. But if it’s already wrecked, gaining information is a worthy endeavour. 

If you just want a mug that works, it’s going to be way less time consuming and frustrating to make a new one. 

[Roberta12]

I have had about 50% success with reglazing and refiring.  If the place is on the interior of a bowl or cup, I simply put more glaze on it and fire away. That is very successful.  If it is on the exterior, I set the piece in front of a small heater or use a heat gun to warm the piece, then quickly put the glaze on.  For me it depends on the glaze and where I am trying to reglaze on the pot.   @Callie Beller Diesel had some excellent points about the underglaze.  But....as @Bill Kielb  said, you don't know until you try!

 

[Ben xyz]

Thanks for the responses! I figure I will likely treat this first re-glaze effort purely as an experiment. Maybe try the underglaze on top, bisque fire (for better adherence?); then satin clear at cone 5. Will later repeat building the same form, but with the revised glaze choices I feel good about. Interesting term "eutectic" btw...have something to perhaps stump the glaze teacher with.

Edited October 3, 2023 by Ben xyz
Clarification