HELP anyone seen these kinds of cracks before?

[jaydubbb]

Seems like they’re only on the surface and they don’t appear until after a kiln cycle. Never seen this before in 5 years of blowing glass and I’m not exactly sure how to prevent it. Any tips? My best guess is that it’s just a bad batch of clear because I’ve done countless pieces that were similar and never had this happen. They are made from China clear but I’ve used China clear for years and never seen this before. If the answer is “buy schott you fool” that’d be a relief sort of. Anything you guys can tell me would be appreciated much love to every one of you :) hopefully I attached these pictures correctly

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[PyroChixRock]

was stuff touching in the kiln?

[nineteen73glass]

yep, put back in kiln and run a flame over it it will be gone immediately

Keep in mind that the molecules of glass are constantly moving and if there is something touching it or if there is a weird crease in the glass or something it changes the movement of the molecules and can cause many different things to happen including little stress cracks like that.. Glass is a wonderful thing!!

I like the piece!

[Kovacs Glass]

And don't buy Schott, the artistic stuff is garbage. Buy Simax!!

[jaydubbb]

And don't buy Schott, the artistic stuff is garbage. Buy Simax!!

I buy Chinese tubing and sometimes pieces will touch in the kiln, does that cause problems? I’ve always figured it wouldn’t make much difference and haven’t noticed it being a problem before. The cracks don’t melt back in very nicely either I’ve snuck my handtorch into the kiln to try to fix those but it kinda makes them worse. Is this why people diss China tubing? For years I’ve just assumed that boro is boro and I’ve made some crazy complex pieces with China clear and never had a problem till like the last couple weeks

[MUPH]

I buy Chinese tubing and sometimes pieces will touch in the kiln, does that cause problems?

I stack production work made with china clear all day long in the kiln and I've never had a problem like this. It could be a batch issue like you mentioned as well. Those look more like scratches in the glass to me then cracks but it's hard to tell from a picture. FWIW, I only use china clear for production. Anything with a weld and I'm going to Simax, or in a pinch, Schott

[Swim]

I have seen two batches of asian clear with this problem, I had a whole case of one inch tube last year that did this to about 80 spoons I made in three days, it was really bad, and I have seen another blower that uses this forum have the same thing happen with a case of 50 mm. its a bad batch, I would stop using it, throw it out. edit- took a year to give that shit away lol

[Swanglass206]

to be just in a few spots makes it seem like there were specific spots of stress or temperature differential/
I would repeat the question of if anything in the kiln was touching.=, and if they were, if the temperatures had been equalized inside the kiln before toughcing.
i stack spoons in the kiln like 4 or 5 high but always have a spot cleared out to put the newest pipe so it can get to the same temperature as the rest of the glass in the kiln. then stack it only once its been in there for a few minutes

[nineteen73glass]

Alright, so last night I was melting glass.. and while I was putting a piece in the kiln I was thinking of these hairline cracks.. I remember piece of mine years back and a couple others that did this and the only thing that I think caused it was my hot-fingers. I am curious if cold hot-fingers touching glass that is not at a specific temp might do this.. I know that is what I thought when it had happened to me.. do you use hot-fingers at all? could it be your cause? Or I might be completely wrong.. lol

[PyroChixRock]

I'm thinking you're right, 1973glass

[Swim]

some things you dont want to believe til you see it, but you can get clear from china that checks under an annealing cycle. I only threw away that case a few months ago or I would send some out for people to sample

[BORO]

I think its just stress. I have seen this countless times. Its only ever the outer third of the wall thickness. Its always conventional cracks that can heal clean. It usually happens to me when I'm in a rush.

I would put it in the same category as frosted glass. A.k.a. Its a product of improper technique. It can be easily healed.

I never did decide if it comes after the kiln cycle, or before. They are so hard to see, they usually get found after. (I have seen them on a complicated build, mid build)

[nineteen73glass]

those cracks he has shown are not Checks though..

[BORO]

If I have something similar....

I will ramp it up to 1100, and just be about getting it in a flame quickly.

The fact that the o.p. Had issues fixing them surprised me. Especially in a hot kiln.

[istandalone24/7]

a propane torch (dab torch?) will heal those types of cracks pretty quickly as well. just be careful sticking a handheld propane or butane tank torch into a hot kiln....i came close to a catastrophe doing just that last summer.

[jaydubbb]

I’m with SWIM I make a shitload of tubes like these been doing production lathework for years and the only explanation I see is a bat batch of clear. I stack tubes but I keep a space to equalize temps first. I have an overly cautious annealing cycle and the cracks aren’t full cracks, just weird surface cracks. So when I try to melt them back in in the kiln they trap air. A full crack would melt back in from the outside to inside. It wasn’t even a full case of tubes, in a box of 60x5 I used the first 5 sticks before seeing any problems, the last 3 had these problems. Makes me not even wanna use China anymore. But when it comes to filling your truck with tubing you really gotta stack chips if you wanna fill it with simax or schott I pay $1 per pound for Asian clear

[jaydubbb]

In my original post, the tube with the yoshi green horns was the one I tried to repair. The first set of surface cracks meted in ugly then a new set of surface cracks appeared around the edges of where I tried to melt it back in. It’s a mystery and I don’t wanna blame China if it’s something I’m doing wrong. In my 5 almost 6 years I’ve never had a problem with China clear that wasn’t my fault for the way I worked it. This is new territory