Sad Times: Black Underglaze Chipping after Bisquefire.

[CFlowers]

https://imgur.com/a/UOSkElv

I recently got a batch of some sgraffito bisqueware back from the kiln (I do not operate the kiln, someone else does).  I painted black underglaze onto leatherhard 06 clay. For the first time, I used Amaco Velvet Black (in the past, I'd used Speedball). There were some mugs, some earrings, small plates, etc. wit sgraffito. Several of the items had chips in some places, especially my bat pie plate.  I've never had this happen before.

Was it me? Did I just make the underglaze too thick in spots? Was it a kiln thing? The person who operated it did seem...distracted that day. But I can't see it being the kiln.  Is there any hope if I dremmel it and then paint black underglaze (thinned and wih real drying between). Or should I dremmel it and then just use my black matt underglaze on all portions except for the bottom of the pan which luckily did not chip off at all.

Also, I broke off a piece of the handle I think I will attempt paperclay that I just saw when searching about reattaching pieces.

Finally, I asked a subreddit the same thing I'm asking here and someone said "Underglaze is not meant to be a coating" I can't tell if they meant "it's too thick" (e.g. coat versus cover and it's a matter of semantics) or if by coating they mean the amount of surface area I used underglaze on. But, lots of people "coat" or cover large pieces in underglaze to carve into.  If it had been you, how would you have done this project?

 

[oldlady]

underglaze is not designed to go into the world without a coat of glaze.     whatever else you mean by thickness, surface area are immaterial.

[liambesaw]

Some of those areas look like they could possibly even be lime pops.  Looks like shards of clay actually popped right off.  Did you make this on drywall or do anything with plaster?  Does your studio use plaster? Is this made with reclaim/recycled clay?

[Min]

It looks like you have a couple things going on. Underglaze looks really thick causing the lifting / shelling plus maybe some lime pops like Liam said. Slight chance it might be shivering and pulling some clay with it but it doesn't looked bonded well enough for that. Can you flake off some bits of underglaze if you try and pick at the edges where it has lifted? If you want solid coverage then 3 thin coats are better than 1 heavy one. Did you water the underglaze down or use it straight from the jar as is? Let the underglaze dry between coats. I'ld try again on some test pieces using less underglaze. Also, have you tested the Amaco underglaze with your covering glaze? I wouldn't try fixing the bat plate, I'ld put it aside for now, run some tests and make a new one. 

[Babs]

Could try grinding/ sanding the black bisque pot. Wash and dry  and apply underglaze to bisque if really trying to save pot.

Handle wise for own use .glaze and fire and glue after glaze firing. How to support it in kiln another matter.

Spooze has worked for many...

I wipe ,with damp brush , entire pot prior to underglazing. Could your pots have been a tad drier than usual?

[CFlowers]

Hi everyone, thanks for taking the time! I'll try to respond to things

1.) No, I didn't use plaster.

2.) To be perfectly honest, I don't remember if this was some clay I had reclaimed from my own fresh bag or fresh clay straight from my bag.

3.) It wasn't very dry when I actually created the sgraffito. It was leatherhard/at the perfect stage of drying. Actually, this was my best sgraffito'ing I've ever done. Le sigh.

4.) I totally could have slapped on the Amaco Underglaze too thick. I DO tend to get "paint happy" and I should have more patience between coats. It's very easy to just paintpaintpaintpaint

5.) I do water underglaze down as needed. Perhaps it needed to be watered down a bit more. It was kind of creamy. Underglaze has always been odd to me. What consistency SHOULD it be? The same as cream and regular paint?

 

But the biggest question I have is to Old Lady....What do you mean that underglaze isn't meant to go out without glaze. Don't many people use underglaze on their bisqueware in order to do that method of sgraffito?  How would you have gone about this project? How would any of you?

[liambesaw]

Well I can't think of any firing problem that would cause this, amaco underglazes are meant to be used from cone 06-10.  Amacos black underglaze is fairly refractory, so if you use too much, you can have issues during glazing as well.  If you had success with speedball underglaze, it may be that speedball is less refractory, so putting a bunch on may not cause issues, but with the amaco vugs and lugs, your normal amount may be "too much".

[CFlowers]

4 minutes ago, liambesaw said:

Well I can't think of any firing problem that would cause this, amaco underglazes are meant to be used from cone 06-10.  Amacos black underglaze is fairly refractory, so if you use too much, you can have issues during glazing as well.  If you had success with speedball underglaze, it may be that speedball is less refractory, so putting a bunch on may not cause issues, but with the amaco vugs and lugs, your normal amount may be "too much".

Yes, that is probably it. Thank you for taking the time to read and respond to my post. I really appreciate it. Poor ole bat pie plate. Alas. I may just make another one. I learned a lot makign this one and now I know how to do it quickly.

[liambesaw]

15 minutes ago, CFlowers said:

Yes, that is probably it. Thank you for taking the time to read and respond to my post. I really appreciate it. Poor ole bat pie plate. Alas. I may just make another one. I learned a lot makign this one and now I know how to do it quickly.

You can always try touching up the chipped spots with more underglaze.  It's fine to apply underglaze to bisque

 

[CFlowers]

Yeah, that's what I'm doing. Literally right now at my desk, hah.

[Bill Kielb]

1 hour ago, CFlowers said:

Yeah, that's what I'm doing. Literally right now at my desk, hah.

You will likely see the difference in color of the touched up areas. You may be able to blend carefully outward or I have successfully made it look intentional with a different shade and random pattern. The latter was always more successful than the blending I’m afraid.

[Min]

11 hours ago, CFlowers said:

5.) I do water underglaze down as needed. Perhaps it needed to be watered down a bit more. It was kind of creamy. Underglaze has always been odd to me. What consistency SHOULD it be? The same as cream and regular paint?

I use a little bit of Amaco Jet Black V361 on soda fired pots, 1 brush stroke stays black and 2 coats is a very solid black. It's pretty concentrated stuff. I dilute it  approx 1:1 water to underglaze but I just eyeball it, it's not drippy off the paintbrush. I'ld really suggest making up some test tiles, apply the underglaze with 1, 2 and 3 layers and try your clear glaze with them and see how they look. 

Vase below has 1 brush stroke of Amaco Jet Black around the flower petals and in the centers of them. Even with just one coat of diluted Jet Black it's still very black and solid.

 

[oldlady]

Just now, oldlady said:

cflowers,   i did not see this until today, may 22 so believe me that i was not ignoring your question.

underglaze that is not glazed will pick up every bit of grease possible and with handling change from a flat color to one that looks like a dirty, unwashed piece.  your pie plate would be ruined by the oils in your own hands if you left it without glaze.  your pie plate is very imaginative and i like the handles particularly.  that is what i meant.

 your sgraffito work is well done and you applied it at the correct time.   i have done sgraffito for many years at the stage you did.   i cannot imagine trying to cut through a thin coating of underglaze on a bisque piece, though.  just the sound of a metal tool on that surface would be like scratchy  chalk on a blackboard.

there was a well known potter, Charles Counts,  who wrote a book, Pottery Workshop, in 1973.   it covers the topic well.  i was fortunate enough to meet his apprentice who taught me all she could.  in 1984 i attended a week long class at count's studio where i discovered that because he worked almost exclusively in slipwork, he had the various colored slips in large trash cans.  it was easy for him to get an even coating by dipping each piece into the wet slip.

i apply mine by brushing while the piece is on a wheel so the coating is evenly applied.   i can also spray the slip while it is spinning on a banding wheel.   it is easy to determine thickness by either of these methods, just a tiny scratch will show through to the clay surface.  you might look at my albums to see the many bowls i have done and am still doing to get some idea.  yes, there is a glaze on every piece.  

 

[CFlowers]

On 5/22/2020 at 11:31 AM, oldlady said:

 

 

Thank you!! And I love your bowls. I am going to give the bat plate another go.

[Bill Kielb]

2 hours ago, CFlowers said:

Thank you!! And I love your bowls. I am going to give the bat plate another go.

Just a note, per below you can do many many things with underglaze. Here are some ideas. Your imagination is the limit!

• ombre lidded jar, underglaze ombré, clear over top, liner white interior.
• sugar bowl painted underglaze with matte overglaze
• Ikebana underglaze painted design with celedon green gloss overglaze
• painted holiday trivet with matte clear overglaze
• trinket box painted Symmetric  design with clear gloss green celedon overglaze
• Painted golfer underglaze with matte overglaze and liner gloss glaze interior.

 

 

[CFlowers]

15 hours ago, Bill Kielb said:

Just a note, per below you can do many many things with underglaze. Here are some ideas. Your imagination is the limit!

• ombre lidded jar, underglaze ombré, clear over top, liner white interior.
• sugar bowl painted underglaze with matte overglaze
• Ikebana underglaze painted design with celedon green gloss overglaze
• painted holiday trivet with matte clear overglaze
• trinket box painted Symmetric  design with clear gloss green celedon overglaze
• Painted golfer underglaze with matte overglaze and liner gloss glaze interior.

 

 

wowwww!