Wednesday, June 17, 2009

Bare with me or the naked truth about our glazes....

I know, I know.
No one is getting bare here but maybe some pots.
Seriously folks, life can be full of ups and downs and I felt them all today.
Some of the kiln was good and some of it was bad and some of it was just mediocre.
I would love to have some nice pots which I really wanted to take photos of, but this load just did not do that for us.

We are having problems with some of the glazes.
What can I tell you is, after no crawling for months, we had several very nice pots where the Tomato Red glazed crawled under the wood ash glaze.
Sigh, breaks my heart.
Oh, there were some good pots in the load but all I can see right now are those darn seconds.
I have to deal with the losers before I can move on.
We are going through all the variables; firing, glaze, what's different- why has it been working and now it's not?
Why did most of it come out the color of mud?
I have no confidence in what we are doing with this glaze.
All I can think of is to toss it out and start all over again, which we have done more then once.
We have taken this glaze apart before.
Now I do need to tell you that up until about 2 years ago we never and I mean never had any trouble with this glaze.
Or the other one which is crawling as well.
The other one will crawl out of the blue.
With 10 mugs on a shelf 4 of the mugs crawled and 6 did not.
Same shape, same size, all glazed at the same time.
It was not where the mug was sitting on the shelf.
Why do I think that? Because it would be one towards the bag wall- okay maybe some flame, but then explain the ones in the middle of the shelf???
It is driving me batty.
The common ingredient here is wood ash- could it be the wood ash???
We plan to take apart these glazes again and go over all our notes.
what has changed?
Or are we dealing with gremlins?
So I am posting up the crawled vase any suggestions.


Shortstuff said...


Amy said...

It's great to have discovered this blog and the forms on this post are just gorgeous. Hope you find out what you want to know about the glazes; sounds so frustrating!

Jay said...

From the pictures it looks as if there is a problem with the bisque, because there are such large crawled areas. Maybe the bisque is developing areas that are not sufficiently porous.

Assuming that you are confident of the bisque and that you are not seeing drying cracks on the glazed ware before firing - - if nothing else has changed, there may have been a change in the composition or preparation of one of the materials going into the glaze. If something is milled finer than it used to be, that can cause crawling. It is rare to see a glaze high in iron oxide crawl due to shrinking or cracking; iron oxide glazes usually apply very well. Since the color of the glaze is changing - - too muddy - - I suggest looking first at the whiting or other calcium carbonate source in the glaze, since calcium has a tendency to bleach the color out of iron oxide.


I had problems with a glaze I'd used for years, mixed exactly the same as always. The problem turned out to be the water - the chemical changes in the tap water I used to mix it up when they started adding flouride to the water supply acted with the glaze to ruin a perfect mixture that had worked for years. I now only mix my glazes with distilled water. It's expensive when mixing a large batch, but much less trouble than ruined pots and all of the disappointment and time trying to reduce all the other variables to fix the glaze. I'm so sorry for your disappointment!

Judy Shreve said...

Meredith, I am so sorry! This is the most frustrating part of being a potter.

I agree with Jay that it's probably a chemical in the glaze -- that seems far fetched when it only happened on some of the pots. But because you've determined it's not placement in the kiln, I would look at chemicals first.

Have you recently purchased new chemicals? I've been hearing from other potters about the feldspars changing & I know my recent order of talc is grey instead of white.

I sure hope you determine what's going on soon. Your work is so wonderful!

Jay said...

PS - - I'm old-fashioned and remember when Seagrove potters would sell just about anything that came out of the kiln in one piece - - I would buy those "seconds"!

Michael Mahan said...

I've had a couple of pieces where the glaze crawled, complicated sgraffito designs on them. This particular glaze seems to crawl unless I raw glaze. Raw glaze, and no crawling. Bisque and glaze, crawling.

Very disappointing.

Sorry for your losses.


Annapants! said...

Ugh. That totally BLOWS! I hope that your detective work pays off and you're able to find out what's going on!

In the meantime, I'm with Jay -- I'd buy those seconds! Please don't chuck them in the pond just yet! :)

Anonymous said...

sorry for your troubles... diagnosing glaze faults is got to be one of the most difficult endeavors because there are so many variables and each potential solution takes so much time and introduces new variables. without knowing and without adding more speculations i would agree that some compound in the glaze has probably changed. i have had trouble with water too before... lime leaching out. good luck

Anonymous said...

kinda wonder if the glaze is mixed thoroughly or there are clumps of something

Gary Rith Pottery Blog said...

man, it must be the f##king MOON o something because I had some stinky problem pieces in the kiln load I just unloaded....maybe it isn't the glaze but the kiln gods are unhappy!!!!!!!!!!!!!!!!!!!!!!

MH said...

I believe I've narrowed the fault down to an overly fine material in the cover glaze. It's and albany/ash glaze and I sieved the ash thru a sixty mesh screen. The glaze underneath has bone ash and magnesium carbonate in it as well as soda spar, flint and kaolin. I've been thru a lot of testing with that glaze because of problems with 3 of the five ingredients. First it was the "free" soda spar that turned out to be finer than 400m . Then it was the bone ash that wouldn't crush well and thus became suspect. (now using synthetic) After that it was the magnesium carbonate that turned out to be at least a third denser than any I had bought previously. It took me almost five months to work through all this just because we don't fire any more often than every 4 or five weeks. I'll get back to ya'll after next firing when I've had a chance to try going back to totally unfiltered ash. It might be a while - I'm building a smaller kiln.