Tuesday, September 8, 2009

nothing to laugh about.

i LOVE fake teeth. i think they make everybody laugh and are a good mood booster. but right now, nothing can get me to laugh. i am having the HUGEST glaze problem that i have ever had. i am getting tiny bubbles and blisters on the entire piece and i can't figure out why. i've done 4 firings in my test kiln (5th one firing now) and all have been the same. it's as if someone sprinkled sand on the entire piece. and this is the same method, the same clay and the same glaze i've been using for 15 years. i tried a new batch of glaze, changed the brush, applied a thinner coat of glaze, made sure there was no dust on the bisque ware, and still BAD. very bad. i'm at my wits end. and i've ruined a lot of custom orders . . . please bear with me. if i can't solve this problem, i may have to change careers. no joke.

any ideas anyone?

16 comments:

HolzDesign said...

Hi! Perhaps it have some thing to do with plaster getting stuck in the clay and when the temperature rise plaster comes out.

rae dunn. said...

but i don't use plaster !! where would the plaster be coming from ?!?!?!

Kip said...

Hi Rae -- Have you purchased any new bags of materials that are used in this recipe lately? If so, that could definitely be the culprit. Suppliers are pretty consistent about chemicals, but there is always some variation. Sometimes they'll change where they're getting a material, or a batch can become contaminated. If you've remixed the glaze with no improvement, I would go to your supplier and purchase small quantities of all the materials you need for this recipe and test again. If that works, then you know something in your studio was somehow contaminated. If new chemicals don't help, then my guess is that your clay supplier changed something, or they got a contaminated shipment.
You'll figure this out!

ang said...

mmm have you double checked the clay body, any stock change there?? tried a an old glaze sample...is the kiln firing properly?
the only time ive had a result closely to what you've described, is when glazes don't match each other on glaze layering, or when a glaze has settled in the bucket during glazing and stirring between dips. small amount of epsom salts has helped keep the glaze in suspension..hope you can nut it out, let us know...ang

Anonymous said...

very strange. are you using a new hand lotion or hair product that might be transferring from your skin to the clay? something that has more oil in it?

Jenn said...

Could it be the clay and not so much the glaze?
-Inconsistencies in this batch of clay, maybe try firing the pieces a couple cones hotter to see what happens.
-There may also be air trapped in the pieces due to a too high density in the clay body.
Although, I have the feeling that you may have already been using this same batch of clay with no problems in the past, so I thought I would just throw the idea out there. I am sorry that you are having this issue-you've probably already thought of this but there is a wealth of info on various different message boards from people who may have dealt with a solved this very issue. Good luck!

cindy shake said...

could it be from your water source?

Michele D'Amico said...

We had a problem like that with just one clay. We used several in our studio. It was an IMCO clay & they swore it wasn't the clay but later it came out that they had changed the clay formula for a hugh batch & didn't admit it until the batch was gone & they went back to the old formula. Have you tried the glaze on a completely different clay? Blistering is usually off gassing from the clay isn't it?

Mary Camin said...

New career ??? ... like I've never had that thought before !!! If you've tried a new batch of glaze, etc,
perhaps the clay body is bad. Is it Laguna? (I had a different kind of problem years ago after years of use) Are all the problem pieces from the same clay batch? Have they changed the formula?

Is the kiln firing properly that you can tell — cones ok- not over firing? sorry to hear of your losses ...
i've been there. Not funny at all! Good Luck
BTW ... I've been at parties where the teeth come out, lots of stupid laughs!

rae dunn. said...

all good ideas people, thanks. but fired work definitely from different batches of clay, am VERY aware of not getting hand lotion on bisque, thought of contamination from paint brush, bowls, water...changed all that and still the same. this is a store bought glaze that i have used for so many years. and thats the thing, i've been doing the EXACT same method with same products for a gazillion years and that is why it is so frustrating !!!! even master potter christa assad can't break this case !!!

what's a girl to do ?

Emily Dyer said...

Has anything changed about how long your firings take to get to peak temp, etc.? I had similar pinholes and blisters on a clear glaze that had been very dependable. It turned out the pyrometer in my kiln needed to be replaced and while the digital controller thought it was going to cone 5 it was actually way overfiring. Once I replaced it (and embarassedly started using cone packs in every firing to double check) the pinholes disappeared. It only took a VERY small overfiring to create the problem.

ang said...

i'd be thinking it's the glaze then can you get the batch tested chemically...check with your supplier for sure..

dana said...

I have no idea....but I just want to send you some good energy to figure it out, and some answers soon! good luck, Rae!!

Dirt-Kicker Pottery said...

My last firing I had a simular problem. I think my disaster was caused by two things. My bisque firing barely made it to ^06. My Glaze firing heated up way too fast. My stuff came out with bubbles and pits on almost every piece. There was also a grainy dust on some of the pieces.

Maybe your test kiln is heating up too fast.

When you find out what's causing the problem please be sure to let us know.

rae dunn. said...

emily dyer and the dirt kicker WIN the prize ! my kiln, which is old and worn and used very often had not been reaching temperature, so i had been firing 2 cones higher with perfect results for a long time.....but i had just had that kiln re-wired. and now it fires spot on.

the work was being over fired. pilot error !

duh....it makes so much sense and yet took 7 firings to figure out.

i should have stayed in school and become a doctor like my mom wanted !! there are SO MANY variables in this business. uggghhhh.

Dirt-Kicker Pottery said...

So glad you got the problem figured out. It's so frustrating to lose kiln loads of pottery.