Hey all. I'm relatively new to lampworking. I am self-taught (trial and error), and have been making borosilicate pipes for about a month now.
A gigantic problem I have been having is that everything always cracks on me.
Let me elaborate, here's my current technique:
1) Pull a point
2) Pour frit in to tube
3) Seal end, blow out into a bulb
4) Melt frit on to the inside
5) Add twists, bulges, etc to the pipe shaft.
6) Pop a hole for the bowl/carb, and make the bowl.
But here's where the problems begin. When I go back to the point to create a mouthpiece, it usually ends up cracking off. I never had this problem so often before I used frit.
Not only that, but after the pieces cool, they develop a few cracks. (I usually air-cool then bring up to annealing temperature in my kiln)
And as if THAT wasn't enough, when I try to repair the cracks by bringing the borosilicate art piece up to 650 C, and reintroducing to the flame, it just starts cracking more when the flame touches it, as if I didn't preheat it at all.
Now, I should note that I do like adding twists, and this may or may not contribute to the cracking.
Here are some examples.
This one worked out perfectly, except it has one small crack where the bowl meets the shaft (Likely a difference in thickness)
http://yfrog.com/n6earth012j
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This one cracks lengthwise from the black head. I repaired all the cracks, but after cooling, it had cracked again.
http://yfrog.com/n1parasite011j
I'm probably missing some elementary knowledge. Don't leave anything unexplored.