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Amaco Underglazes And Crawling Issue


moh

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Hi all,

I've been starting to have a crawling issue with 3 of my last firings and can't figure out what's happening here (see photo).

 

All color underneath the clear ^5 glaze is Amaco Velvet. I give 3 good layers for the underglaze every time, and have not changed the technique for painting. Glaze and clay body also remain the same.

 

Upon suggestion from a friend I tried doing the firing SLOW, but that didn't help either.

 

Couple of questions for you Amaco veterans:

1. Have you had issue with the crawling happening over Velvet? How did you resolve it?

2. Even in small coverage areas, the glaze is up higher where there is no underglaze, and lower where there is.

 

A bit lost on what to do about this new strange issues.

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Ouch, what a shame! lovely painting on those.

 

I don't use Amaco ugs but throwing out a couple guesses here. Underglazes too thick, do you dilute the first coat and let layers dry in between coats? Ware picked up some dust before underglazing / glazing? I would try putting the ugs on greenware. I use mostly Spectrum ugs on greenware, some of the colours flux a fair bit by ^04 which makes glazing them a bit more fiddly to get a thick enough coat on. Don't know if any of the Amaco Velvets do.

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I use a lot of Amaco ug.  I do use it mostly on bisqueware.   I have not had the crawling issue, but for the work I do, I usually dilute the ug a bit and then blend it with other ug.  Like Min suggested, could your  work have picked up some dust?   Could it be too thick?  As with other products, if you contact Amaco, they might be able to give you some suggestions.  Your pieces are knock out beautiful!  You need to figure this out!!! 

 

Roberta

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I use a lot of Amaco LUGs and Velvets. I almost always paint on green ware not bisque and have not had an issue with crawling.

 

A couple questions...

 

Do you rebisque to set the UGs before glazing?

What Clear are you using over the tops of the UGs?

 

If you are not rebisquing I would try that to set the colors. If you are rebisquing then I would try painting on greenware and bisque firing before glazing as usual.

 

I am using Amacos Zinc Free Clear. It wants to be THIN, one coat very thin and it's happy. If you are not using this, maybe buy a pint and give it a shot.

 

I would do those tests and see if that fixes the issue. If they don't then I would try thinning my first coat down, paint on greenware, and use Amaco Zinc Free Clear and see if that fixes the issue.

 

Your work is lovely I hope you can solve the issue quickly and DO LET US KNOW so others in the future can find the answer that worked for you and be helped as well.

 

T

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sorry no answer here either.

 

but more questions. in the first orange cup did u use orange ug and when the glaze crawled it showed the white body on it? what i am trying to understand in that picture is did the glaze 'leach' out the ug leaving clay body or next layer of ug exposed?

 

is the same thing happening in the other cup? did the green of the ug crawl along with the glaze? did some black leach into the glaze staining it?

 

the only difference i have found in my limited use of ug - on greenware - no seeping of ug onto clear glaze. but if i used ug and then dipped glaze right away there would be some leaking of ug colour into the glaze where the glaze was the thickest (when i discovered that i used it to my advantage and made great icecream bowls).

 

have you changed anything? is everything all the same and suddenly you see crawling happen?

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This strikes me as a chemical reaction: more than just the usual crawling. The ear on the panther crawled exactly on the "ear" outline: very abnormal. On extreme and rare occasions have I seen glaze "ball" up in pools. Crawling typically just pulls back into the body of glaze. Something is causing this.

 

Nerd

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Glazenerd... good eye. It's got me wondering are you by chance sketching out the design with something then painting the underglaze over it? If so is it possible there is a bit of wax in it? I know some pencils use a waxy type binder to hold them together and this could be making the underglaze pull away from the drawn lines.

 

Just another thing to consider.

 

T

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in agree with nerd. I looks like the areas may be where the underglaze brush strokes may have been thicker. IS that a possibility? CAll Amato and ask to send their tech these pictures. maybe he can advise. THey give workshops all the time and support their products. I am sure they'd be helpful.

 

MArcia

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Thanks everyone for the responses.

I'll just post reply to all the comments here at once:

 

- I don't use lotion, so that would not be the issue.

- Clay body is Georgies Trillium, and glaze is Georgies Super Clear.

- UG is painted 3 coats on bisque for solid coverage, the rest I use usually 1-2 undiluted stroke.

- I do use a regular pencil #2/HB pencil to do all the outlines.

 

Process of elimination hasn't helped, since I'm doing everything exactly the same (except the pencil. I grab whatever brand is in the store)

The kiln I use is in a community studio setting. Is it possible that there's reaction to someone else's glaze from previous firings?

I'll try the tip of refiring to bisque after painting, and if that doesn't work will try the painting on greenware.

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I have been using Amaco underglazes in my classroom for years.  I have only had a couple issues with them.

 

One is an issue with application.  A student was trying to do drips with underglaze.  They applied waaaaay too much, and it cracked a bit, as it dried/ shrank.

 

The other issue is still somewhat of a mystery.  A student applied underglaze at the greenware stage (This is usually when I have students apply it).  After it was bisqued, some of the underglaze flaked off.  Before glaze firing, the student reapplied the underglaze.  It flaked off again, taking the clear coating with it.  We even tried again, to no avail.  Nothing would stick to those spots.  Posters here suggested that something got on the ware in those spots and continued to act as a resist.  This is definitely possible, and really the only thing that makes sense.  I even had a similar thing happen to a few jars I had made.  I don't remember having anything on my hands, when I went to underglaze, but it is possible.  I do remain cautious, when underglazing/ glazing ever since.

 

I would recommend thinning your underglaze or using less coats.  I treat them like watercolor in some cases.  Build thin translucent layers.

 

Best of luck!

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  • 6 months later...

Hi!
 
Wondering if you ever found a solution to this?? I've been having the exact same problem with my pieces lately but they look more like your first image than the second. I've been looking around for causes/solutions for a while but this thread is the first place where I've seen something similar. 

Thanks!

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