Cause of blotches? - WarmGlass.com

Cause of blotches?

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lmartine
Posts: 36
Joined: Sat Mar 30, 2013 9:05 am

Cause of blotches?

Postby lmartine » Sun Dec 22, 2013 5:33 pm

Hi again,

After I cold worked my chessboard using a 400 grit handblock, I cleaned the project in lukewarm water then dried it. That is when I noticed for the first time that there were blotches on all the clear squares (not really apparent on the driftwood squares - but that may just be because of the color). That side of the chessboard was down on the fiber board, so I do not think that it is devit. I had vented the kiln between 900F and 1100F as this was a new fiber board.

What caused these blotches and how do I get rid of them? Somehow I do not think that they will 'disappear' when I fire polish the project ... or, will they?

Cheers!

Lucie
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blotches.jpg

Valerie Adams
Posts: 587
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Location: Santa Rosa, California
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Re: Cause of blotches?

Postby Valerie Adams » Sun Dec 22, 2013 5:37 pm

Was the clear glass Tekta?
I've found that Tekta doesn't play nicely with Thinfire, but it sounds like you used a thicker fiber material than Thinfire.

Did you prefire the fiber board? Looks like contamination from organic materials that didn't burn out of the fiber.

Drewcilla
Posts: 60
Joined: Fri Apr 11, 2008 9:10 am

Re: Cause of blotches?

Postby Drewcilla » Sun Dec 22, 2013 6:32 pm

I had the same problem with a plate. I, too, tried sanding and even etching. Finally I cured the problem on a fifth firing by covering the plate with clear powder and going to 1475.

Good luck,
Drewcilla

lmartine
Posts: 36
Joined: Sat Mar 30, 2013 9:05 am

Re: Cause of blotches?

Postby lmartine » Sun Dec 22, 2013 6:50 pm

Thanks for your replies.

I did not use Papyros or ThinFire. The chessboard was placed directly on the fiber board.

I have just spend another 45 min cold working it again but this time with 200 grit. It is now nearly all covered with these 'blotches', sooooo.... Am I right in assuming that because of the uneven surface of the fiber board, the glass itself is uneven and therefore I sanded at different 'depths' (kind of like etching but with a diamond pad). If that is the case, it would even out when I firepolish it, right?

Lucie

carol carson
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Location: Portland OR
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Re: Cause of blotches?

Postby carol carson » Sun Dec 22, 2013 7:07 pm

The marks look to me like they are from the cold working. You said you are doing it by hand right?
In my experience it just takes a lot of hand work to get past the point of the marks being left.

Laurie Spray
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Re: Cause of blotches?

Postby Laurie Spray » Sun Dec 22, 2013 10:03 pm

I would fire it to around 1400. Safeguard it with a devit spray or a light sprinkling with clear
powder.
Laurie Spray

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charlie
Posts: 961
Joined: Mon Mar 10, 2003 3:08 pm

Re: Cause of blotches?

Postby charlie » Mon Dec 23, 2013 1:25 am

the board wasn't smooth. the hand sanding only hit the high spots. what is the backing of whatever you're sanding with? if it's not hard, then it's flexing over the high spots and skipping the low spots. you might try backing it with something hard, a piece of 2x4 or something, so you can get it even. if not, when you firepolish, the low spots will probably still contain some fired in fibers, and thus cause some sort of devit. the other way to do this is to do a light sandblast instead of handworking. that will get it evenly abraded (although will still contain low/high spots), which will go away when firepolished or full fused in a 2nd firing.


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