Razor blade - very carefully.

Katydid, I'm new to this forum, and I read your post and saw the photo of your broken gazing ball. I just finished a fundraising workshop at our church, and we completed 35 mosaic gazing balls using old bowling balls. They were absolutely beautiful. If someone could tell me how to post photos on this forum, I'd try so you can see some of them. I became the official "grouter" because no one was ever comfortable enough to try it. The glue of choice for our group was Liquid Nails - clear or putty colored - sold at our Walmart. I found it very important to use the correct amount of glue. Apply enough on the marbles or pieces of glass so the glue hugs the piece but doesn't fill up the space between the pieces. Several pieces would come off during the grouting process if the pieces are glued improperly and most likely won't hold up outside from year after year. Good luck with your project. It was the most fun our group had crafting. We're gearing up for our Fall Craft Fair - this will be our 5th year and trying to come up with ideas for crafts/art to sell. Anyone out there have any good ideas and photos would be very helpful. Thanks very much!

"mix two tubes together" That is very likely epoxy. The short setting epoxy ('5 minute') is often not very waterproof, but this does not sound like a 'wet' application.

here's the web site: thistothat.com this is such an awesome site, it lets you choose one thing to glue to another and tells you what kind of glue to use.ENJOY