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other reason for pinholing during application?


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#1 yarddog

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Posted 10 May 2013 - 10:33 AM

I know the reason usually cited for pinholes is too-thick glaze.
I am not referring to the pinholes that appear in a glaze firing; I mean the bubbles/pinholes that are left on bisque ware after dipping in a glaze...

The glaze in question, a cone 6 white, is fairly thin already, but leaves multiple small pinholes. The obvious answer would seem to be that I stirred too vigorously, and introduced a lot of air into the glaze. I have tried stirring very gently, to prevent air bubbles, but they seem to happen with this particular glaze anyway, almost as if the air bubbles remain in the glaze from day to day. I first mixed this glaze a week ago...
I am able to stir other glazes with a drill or, in small quantities, a hand blender, without problem.
Why would a particular glaze need to be stirred more gently?
(Very much a newbie at this, having just mixed my first five glazes, so any advice much appreciated.)

#2 Marcia Selsor

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Posted 10 May 2013 - 10:40 AM

you can eliminate bubbles from vigorous stirring by spraying diluted alcohol on the surface. It breaks the surface tension.
It works for plaster as well. Also you can bisque fire a little higher and longer like to 04. The clay won't suck up the glaze as quickly.

Marcia

#3 neilestrick

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Posted 10 May 2013 - 10:54 AM

Do the pinholes melt out and smooth over in the firing? If so , then don't worry about them.
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#4 yarddog

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Posted 10 May 2013 - 12:09 PM

Wonderful suggestions. Thanks so much.

you can eliminate bubbles from vigorous stirring by spraying diluted alcohol on the surface. It breaks the surface tension.
It works for plaster as well. Also you can bisque fire a little higher and longer like to 04. The clay won't suck up the glaze as quickly.

Marcia





#5 Mart

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Posted 12 May 2013 - 12:57 PM

Just use your finger to smooth those over and your are good to go.
BTW, maybe you need to water down the glaze and apply it in few thin(er) coats?

#6 Marcia Selsor

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Posted 12 May 2013 - 01:10 PM

You can also glaze after washing/cleaning your pots so they don't suck up the glaze as quickly as if they were really dry. You would need to use precaution if the piece is thin. Then it may not dry enough to absorb the glaze.

Marcia

#7 Min

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Posted 12 May 2013 - 02:58 PM

If your glaze has spodumene in it that might be the cause of the pins/bubbles. There is a soap residue on spodumene from the processing of it (North American spodumene),causes frothing or bubbles in the glaze that then turn up on the dipped pot. Marcia's suggestion of alcohol works to get rid of them in the glaze bucket, hairspray works too. If your glaze does have spod in a large amount then you can mix up your weighed spod with water and really get it agitated then pour off the water. Since spod is only slightly soluble you don't loose much lithium.

Min

#8 Nancy S.

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Posted 12 May 2013 - 08:11 PM

I've noticed the same pinholing issue when brushing on commercial glazes (not sure if they contain spudomene or not) -- after the glaze is dry, I lightly rub a dry finger over the pinholed areas until they're smooth and they fire just fine, as if the pinholes were never there. Posted Image

I thought it might be a "too vigorous stirring" issue, too -- thankfully, it's an easy fix. Well, relatively easy...in corners it's harder to reach those spots, or the areas right next to sliptrailing. The pinhole-bubbles I've left do NOT smooth over in the firing, unfortunately.

I found a makeup smudging tool that works well for getting in areas that are smaller than my fingertip. Q-tips also work; just watch that the cotton doesn't stay on the piece.

I think it's just an absorption issue - the clay sucks up the moisture too fast in some areas, causing the pinholing. Lightly sponging bisque ware helps a little, but it depends on the piece.




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