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Hello

I often have problems with crawling, I have been reading about adding adding a small amount of Veegum CER or CMC to glazes to help them adhere to the clay, has anyone had else tried this or have this problem?

I make sure there is no dust on my greenware pots but wiping them with a clean sponge before glazing (I dip glaze, not brush on).

I've been experimenting a lot with layering glazes, and getting some really lovely results, but often at least a few mugs or 1 bowl out of a set will have crawled! Very frustrating, and I feel I can't go on loosing 20-30% of each kiln load.  Sometimes I've found things that are in the middle of the kiln shelf are more likely to crawl which seems odd! I go up to 1230. 

One of the main glazes I use is Amaco Tourmaline which I put on top of an oatmeal or ironstone.  Any advice appreciated!

Thanks, Sophie 

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Hi Johnny, thanks for the reply. Yes here is a photo of one that crawled and one that didn't.  I do notice that it tends to be on a curved decent, for example on bowls it happens on the outside as the side of the bowl curves down the foot (hope that makes sense). 

 

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Edited by Sophie D
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9 hours ago, Sophie D said:

I have been reading about adding adding a small amount of Veegum CER or CMC to glazes to help them adhere to the clay, has anyone had else tried this or have this problem?

Gums will help with the adhesion of the glaze layers if that is the cause of the crawling but there are other things to look at with crawling glaze problems too. Overall thickness of the glaze layers and also how well the top glaze is bonded with the base glaze are things I would be looking at here too. If there are cracks or lifting of the dry glaze then chances are it will crawl when fired. If you add gum try for the least amount you can to solve the problem. I'ld suggest mixing up a very small test batch of 100 or 200 grams of base plus water plus 1/2% of CMC or Veegum Cer. Try it with the gum in just one of the glazes first then layer the other glaze over it. Dip a few test tiles for the same length of time you dip your pots. (test tiles should be same thickness as your pots and bisque fired the same) Now add some gum to the second glaze (again just a small test batch) and dip some more test tiles. Get the second coat of glaze onto the test tiles as soon as the wet sheen is gone and you can handle the pots. Don't wait for the base glaze to dry all the way. Glazes with gum will take longer to dry so using the least you can is a good idea. If the 1/2% isn't enough then double it and try again, it might take up to 2% gum. Decreasing the water content of the glaze sometimes helps with thin walled pots too.

Since you are using commercial glazes we can't look at the recipes for those and adjust clay content etc.

If you can get a product called Magma in the UK then I would try that, if not then try either CMC or Veegum Cer.

Edited by Min
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@Sophie D are you buying your glazes pre-mixed in containers, or buying dry glaze and mixing it yourself? Pre-mixed glazes are made for brushing, and already have the gum and other binders which make them brushable. So if that's the case, then the crawling is most likely an issue of application. If the first dip is too wet or too dry when you do the second dip, the glaze can lose grip on the clay and crawling happens. Pre-mixed wet glazes have a higher water content than glazes that are mixed from dry materials, so they'll take longer to dry. After the first dip, the pot must be dry enough that the clay can take in more water when you do the second dip. A thin pot will have to dry for a really long time before doing the second dip because it becomes saturated with the first dip. However, if you wait until it's totally dry, then the glaze layer itself will take in the water and lose its grip on the clay. There's a sweet spot in-between, and it's a pretty big sweet spot really, when the second dip should happen.

Also, if I remember correctly, Oatmeal is notorious for cracking as it dries.

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