need help with cracking marbles

[hamburger]

hello, i just started lampworking last week and ive made some mushroom and compression marbles. i am using borosilicate glass 14mm rods, northstar color and a gtt lynx torch. the last 3 compression marbles have split in half about 10-15 minutes after they come out of the torch. i dont have a kiln right now, can i use a fiber blanket on 1" marbles? would they be cracking because im not heating it good enough? what northstar colors should i be practicing with since i boil out alot of the ones ive used so far? thanks for any help

[loco]

I might suggest posting in the boro room, you may get an answer a bit sooner. Wish I could help, but I don't work a lot of boro and when I do I put it in the kiln right away.

Here's the boro room:
http://www.lampworketc.com/forums/forumdisplay.php?f=54

[Kalera]

It sounds like you may not be evening out the heat in your marble before you lay it down. It's not vital to do so if you're putting it in a kiln, but if you're putting it in a fiber blanket you need to "flame anneal" it (doesn't really anneal, but evens out the heat to help avoid immediate cracking) by turning your oxy all the way down and rotating the marble in the outer reaches of the propane flame for a minute. It will get coated with soot; don't worry about it.

[FiG]

Hi Kalera is right on about evening out the heat. A kiln is required to anneal glass.

[Keltik]

"what northstar colors should i be practicing with since i boil out alot of the ones ive used so far? thanks for any help"

I would stay away from the crayon colors (the dense colors that look like crayons or cadnium colors) They work well if you incase them with clear first but just starting out I would stick with the cheapest, lots of clear some cobalt blue, also have some fun with some of the striking colors like double amber purple. Make sure you heat the marble all the way through and stick with marbles under 1" until you get your kiln.

OH and Hi MIke


Dave