If your making a mold, I've had good luck with smooth-ons silicone and urethane materials. Highly flexible stuff and amazing detail capture," moldstar" would probably work, lots of different ones they carry would work. They have glass like urethanes you can use as your casting material, add just a little white dye to get it to look like milk glass. Stuff is pricey though but I don't think you need much.
I've never tried this to repair a globe, but I could see it working.
Last edited by Paul Bell; Thu Jan 21 2016 01:01 PM.