Somebody on the crafting forum was mentioning cracked marbles a while back. I bet it was the same thing. I've bought a few of the cracked marbles at garage sales lately, but would love to know how to make the broken glass. I'd like to try it instead of mosiacing a little plastic pony rocker I have.

I found this on glass marble cracking. Maybe you could use a thicker glass.

cracked marbles (fried marbles) .....old Brownie-Girl Scout project

Rapid change in temperature will make thicker glass crack internally along stress fractures... can look quite beautiful !
... find marbles in toy stores, hobby stores, flea markets . . .also works with glass pebbles from craft store
...the cracks stay inside the marble and crack "inward"...however, some marbles will break, so do more than you need
...don't use extreme heat or they will shatter.... heated too long, they may fall apart in the water
...safety:
........wearing safety glasses during the process is prob.a good idea, but most people didn't
........any broken marbles will have very sharp edges. ... handle very carefully... they can even break later, or if stressed?
HEATING (several options):
...OVEN.... (15-25 min., at 250-275 degrees, till heated through) ... use a baking pan with lip or cake pan, etc. (don't use it again in case any glass slivers get left behind... or line with aluminum foil); one person does 200 marbles at a time this way (or can use a coffee can and then pour the cold water directly in the coffee can)
...STOVETOP...heat in a cast iron skillet or frying pan or even a metal pot? over high heat for several minutes (no oil), rolling them around until a bit of water dropped in pan evaporates instantly...then heat 1 more min. ...a lid should stay on in case they pop too fast?
ICE BATH...use a slotted spoon to take the marbles from the hot water (or unslotted for oven method) and quickly plunge them into ice water (more ice than water because the heat from the marbles will reduce the water temperature...using a large volume of ice-water is good or change water/add ice) . .
CRACKING...wait 15 minutes before handling (that's when most cracking happens although may hear more cracking for a wk) . . once dry, the cracks will be more visible
MICROWAVE method (no ice-water) ... put marbles in a towel and microwave for 2-3 min.... heats them from the inside out, so when they begin to cool they will crack on their own. .. can help them by tapping with a hammer.
FREEZE FIRST method... froze them overnight.... then put them into an empty coffee can and poured the boiling water on them. They cracked that way too! Shaylee
....To attach things to the marbles or to attach them together, use a clear glue that adheres well to glass (Duco Cement, Bond 257 a glue for gems ... 2 hours to dry, 24 hrs to fully cure.)

This way takes a bit longer but the final outcome is worth it ...I had found that when I took the marbles out of the frying pan then just dropped them all into ice water, they did not crack very much
......so next time, I took them out one by one... slowly dropped them onto a wooden spoon containing a bit of the ice water ...and they all cracked like crazy (they sizzled and cracked, and some even made a bit of steam when the hot marble hit the cold water). cyansoma
...so maybe another thing to consider is the size and shape of the pan you're doing the cooling in (as well as the total amount of ice water) ... in other words, the pan needs to be large enough (and shallow enough?) to not crowd the marbles too much when they're put in, so the water can stay really cold??

I'm just lurking in different forums today and found your post. Go here http://forums2.gardenweb.com/forums/junk/ and I'll bet they can tell you exactly how to do it and how to make the mosiacs with the glass. They are really nice folks too. Have fun.

Nancy

i have a memory of my sisters making crackled marbles in the oven and then the sink when i was little. recently, i found on ebay a fried marble KIT that i bought for my sister's 58th birthday, for the memory.

I went to a craft store here - it's like the old "Dimestore " type store. They have so many of the older crafts . I saw a square candleholder on display that was all crackly . I asked about it ... seems it was made of 5 clear ashtrays . One was the base and 4 were the sides. They were crackled in the oven - then ice -- then glued together to make ( what I thought ) was the coolest candle holder ! I never knew the right "recipe" but as long as the glass was hot ... it crackled in the icy water .