Bake marbles at 325-350 degrees for 20 minutes (for more cracking-look, bake at 500 degrees for 30 minutes). Remove and carefully drop into pan with ice and water. Glue end caps to finished marble (w/starter rings) to create bracelets, earrings, pendants, ornaments...(unique and great gift idea)
Learned this on Pinterest and tried it today! Heat oven to 500 degrees and put some marbles (you can put clear colored or clear with color in the middle) and heat for 20 mins...longer is OK but no better... After, put them in a bowl of cold water. I used a regular ceramic bowl and was afraid of shatter but nothing! It just cracks inside and creates GORGEOUS sparkles! Kids loved it and soooooo easy! Give it a try!