Photo: GREAT DIY GIFT IDEA! Place marbles on a rimmed cookie sheet and bake at 325 to 350F for 20 minutes. Remove from oven and place marbles in ice water to make them crack on the inside. (Be smart and wear safety glasses during this step. I've never had marbles shatter, but wearing glasses just seems like a good idea). :-) Use E6000 glue to attach marble to jewelry findings. You can find jewelry attachments at any craft store. Easy-peasy!