Underglaze on Fired Pre-Colored Porcelain?

[Ben xyz]

Hand built a small 12” sculptural piece with Axner Colored Porcelain (light green) and fired to bisque 04, then cone 6. Am not happy with the final shade of green I was left with (no glazes added as yet).  Need to go for a darker shade, but stay completely matte.

 

 Would it work to apply an underglaze at this point and re-fire, either cone 05 or 6? My concern is the underglaze possibly flaking off of the pre-fired porcelain piece. Thoughts? Thanks!

Edited October 3, 2022 by Ben xyz
To make clearer

[Bill Kielb]

Just some thoughts
Sort of out of order and likely won’t stay put on cone 6 stuff. When things are bisque fired they sinter and not fully melt. They are a bit sturdier but not that great. Just curious if you intended to fire to cone 6 and get a very matte finish with your process. If yes, I am guessing the under glaze or in this case the stained body may have lightened up after firing hotter. If the guess is a yes, this is not uncommon and many manufactures provide some relative direction on what will happen to various colors as they fire higher. Some darken, some fade, etc…. Many sculpture artist I know fire their colors progressively hotter on test tiles to see where it no longer is artistically acceptable to them.

Edited October 3, 2022 by Bill Kielb

[Min]

Hi Ben and welcome to the forum. 

I'ld make up a couple test tiles from the stained clay then fire it to cone 6 (you can skip the bisque) then try the green underglaze on those rather than your sculptural piece and fire one to cone 04 and see what happens. Frit based underglazes don't shrink a lot so it shouldn't peel / eggshell off the piece. You run more of a risk of the piece cracking or bloating if you refire to cone 6. Some underglaze will flux enough to be glossy when fired to cone 6 and even at bisque temps some gloss up so do test it first. Stained clays (or underglazes) will most likely be darker in colour if glazed than unglazed.

[oldlady]

to see the color of the piece you have, wet part of it and look fast.  it will dry back to what you see now but in that brief time it is wet, you can see what it would be with a clear glaze on it.   not that you plan to use one on that piece, just giving you more info than you have right now.  

[Ben xyz]

Thanks for the responses! I had indeed intended to fire at 6, since the colored porcelain examples shown were fired at that temp. Spaced on this shade of green when initially ordering it (very close to yellow).  A good idea to proceed with a test to see if the underglaze will successfully adhere at 04 and/or 6 on this type of porcelain.

Had found that lightly spraying a clear oil base matte Rust-Oleum paint on other colored porcelain sculptures in the past (fired at 6) successfully deepens colors and removes the occasional  uneven chalky residue without adding any sheen whatsoever (hopefully won’t cause any archival problems down the line). Unfortunately, this present green shade is just too far off to even attempt spraying (and negating a possible underglaze application). Fingers crossed the underglaze solve will work out. Will let you know - thanks again. Great this forum exists. Questions will ALWAYS come up!

[Ben xyz]

It worked without a hitch! Used Amaco underglaze (x2) on the pre-fired cone 6 colored porcelain; then fired at cone 06. Got the color correction along with the flat surface I wanted on the sculpture. Thanks for all the help.