I’m props mastering a show called “Slave Shack”, at the Algonquin Theatre in the Gramercy Park area. One of the scenes calls for the actress to fling a scotch glass against the wall, where it breaks.
I decided to buy a number of thin glasses and spray them with Plasti-Dip. It’s a rubber coating which sprays on, and it comes in a variety of colors, including clear.
The rubber coating keeps the pieces of the glass together when it is smashed. If any pieces do break loose, they are not as sharp. I made a video to illustrate the process a lot more succinctly:
The obvious disadvantage of this method is that the glass ends up looking frosted. Also, you cannot use this method when you are breaking a bottle or glass over someone’s head. You can use it to coat glasses and bottles which are being thrown or dropped, but you should not have shards of glass, even coated in rubber, flying around an actor’s eyes and mouth.
The advantage? I bought three dozen (36) glasses for about $50 at a restaurant supply store. The Plasti-Dip is around $7-8 a bottle, and I only needed two bottles for this.
Smash Plastic, your other alternative, gives you a clear product, but it costs around $200 a gallon. You also need to make a mold (and buy molding supplies) and spend the time casting all of your glasses.
Sugar glass is great for films, but it degrades too quickly for theatre. Unless you want to be cooking up a fresh batch every night before the show for the next 2 weeks, or however long your show runs, it’s not a very viable alternative.
Glass dismissed!
If you have Thurston James’ prop book, you will note that this is the same idea he uses for breaking glass on stage. He dips glasses into flex-glue. Other props people put a few coats of Rosco Sculpt-or-Coat. As with everything, experiment with whatever you want to try to get the results you need in terms of time, expense, and final appearance.