After Glaze Application Bubbles/Blisters

[scottiebie]

I demonstrated to my beginning throwing students on how to apply cone 10 glazes by dipping and pouring on their bisque ware.  A student noticed after the application was dried, there was small bubble/blisters on the glazed surface.  I told students to leave the surface alone and hope the glaze firing will melt and smooth away the bubbles.  I also showed them how to use their finger to gently rub away the bubbles.

The next day,  I found one of my students trying to sand away the bubbles with a piece of sandpaper.  I asked why the sanding?  And while questioning this student I found out he was a retired engineer and I guess thought it was okay to sand away the bubbles after application.  I was surprised and had to ask how do you gauge how much glaze you might be sanding away/off?  I also said the glaze dust created by sanding is toxic and that the sanding should stop.  I guess the student thought the glazed surface would be hard enough to sand away the bubbles.  This student wants to see what's going to happen to his sanded glazed piece after firing.  I'm guessing his fired results will be an uneven glazed surface with bare clay spots showing through.  Anyone have thoughts?  

[Hulk]

My guess, likely the results will be interesting, maybe very cool, maybe a bubbly breaking pattern, streaking if the glaze moves moderately; chance of yuck, maybe scabby, crawly where the glaze is too thin.

Good oh you stopped the dust.

[Callie Beller Diesel]

It depends on a bunch of things. How thick did the glaze go on in the first place, how even was his sanding, and what’s in the glaze? How fluid is the glaze, and does it in fact move, or is it a stiff one like a shino or a celadon? Also, what kind of sandpaper did he use, because there’s likely some shed grit on that surface now. Carbide or aluminum could have localized bubbling or refractor effects respectively, which may or may not be desirable. In any event, I wouldn’t expect a sanded version will turn out like the test tile at all. 

A tip that comes up from time to time is that If you’ve got a glaze that gets a bit foamy with stirring, you can spritz the surface with rubbing alcohol and the bubbles pop. 

[Callie Beller Diesel]

I’m going to move this question into the Studio Ooperations section so it gets more visibility and response. Please keep us posted on how it turns out!

[Mark C.]

You learn from your mistakes sometimes they work sometimes they do not.

[Babs]

Be a good test piece, either making your advice positive or how to get a special effect..

Some glazez can tolerate fettling drips a nd bubbles.

Hairspray will disperse bubbles on top of glaze bucket prior to dipping. Cheap and doesnt need much, needs to be repeated after stirring.

Some of your bubbles may be evident if glaze is a stiff one 

[Pres]

My first question about such a phenomenon is whether the pot was washed before glazing.  Washing a piece with a damp sponge puts some moisture into the pot that allows for a smoother application of the glaze, often taking care of some pin hole bubbles that get in underneath the glaze rising to surface.  I always wash the pot with a damp sponge, or dip the pot in clean water before glazing.  How I determine which method to use depends on the number of pots I am glazing. The dip wash is fast, and works well if glazing a lot of pots as the first dipped ones will dry enough to glaze as evenly as a few fresh sponge washed pots.

 

best,

Pres 

[scottiebie]

Hello Pres,

I have my students wipe their bisque with a clean damp sponge before applying glaze.  I assumed that my answer of leaving the glaze pinholes alone and let the glaze firing melt down the pinholes or lightly rub the dried glaze pinholes away.  Apparently, this one beginning student who is a retired engineer thought my options were not working for his piece and decided to take it upon himself to try sanding the pinholes away without telling me.  In my many years of teaching, I have never had a beginning student sand off glaze from their glazed bisque.  Now thinking back after my demo, I didn't talk about and emphasize what might happen if you touch, rub, scratch the dried, glazed surface after application. 

Thank you for your insight.

[Pres]

I understand the situation with the student, especially with adults. I used to teach an adult class on Saturdays at the HS where I taught.  My lead in to glazing would always stress that even though glazes were basically not poisonous, if inhaled they could lead to respiratory problems just as sanding bisque or green ware would. I would also stress as you just mentioned that the glazed unfired surface was fragile and fingers could rub off glaze or leave a mark that would show after the firing. Good time to also talk about the  use of glaze tongs to dip or hold when pouring. 

 

best,

Pres

[Hulk]

I'm also washing bisque before glazing, two buckets, one sponge, the second, rinse, but I'm allowing a full dry sun and maybe overnight afore glazing - less dust, ashy bits, salty junk, and I do sand a bit*, by feel, so, there's dust. It's a bit of bother, but chatter marking seems to fill much better when washed.
If ever getting pinholes from glaze moisture displacing air in the clay as it penetrates, will definitely try your damp glaze Pres.
I am bisque firing to a high temp, with a hold, 
I do sometimes a fast dip, then plunge quickly again, but withdraw slowly, when the gelling action is a bit greater at slower speed - if that closes the glaze layer up, I'm happy. I prefer upside down, where there's more glaze at the top of the ware, being first in and last out.

*away outside, with ppe, dust control protocol, etc.

[Pres]

I think the wet dip also requires a certain glaze consistency.  I like my glaze cuticle thin where a dipped hand has the cuticles still visible even though covered with glaze. I use a 3 count dip on most items. I also use a 6" deep storage bin to dip plates in while using claw type staple removers to hold the plates for a dip through the glaze. Large pieces I brush, dip or pour depending on the size and if streaking glaze is problematic for the form. Everyone has their own methods of glazing and those of us that have been doing it for years become set in our tried and true. Teaching taught me more about ceramic problems than any classroom as a student would have. When you have to solve 10-20 or so different problems a day involving clay you do a lot of research, try a lot of solutions and find a few that work. Too bad it wasn't easier!

best,

Pres 

[Pres]

I should also clarify that my pieces are often highly textured with stamping and incising that leaves room for bubbles in the glazes. The techniques I talked about helps with that especially when the piece is flat as in a paten. Slide dipping had also helped here also.

best,

Pres

Edited July 30, 2022 by Pres
added image

[Kelly in AK]

Students new to ceramics are learning a lot (hopefully!) to make sense of everything happening with this process. It kind of boggles my mind when I think about it. There’s really nothing in anyone’s ordinary experience to compare it to. After years of making pots so many things become second nature we don’t even think about them, but for students even the most basic things are like a new world. The beautiful thing is that it keeps getting better the more you learn. Decades on and I still make discoveries, still have surprises both to my delight and chagrin. I hope I never see the day I open a kiln and see everything looking exactly like I expected it to.