When installing new glass crystals sometimes they are held in by a gasket but other times they are held in place by a two part epoxy. The different methods for securing crystals is actually quite diverse. Seiko makes an adhesive specifically for securing crystals but really any two part epoxy will do, so long as it dries clear. It is really easy to mix up too much adhesive. The more you mix up the easier it is to ensure you are using equal parts and therefore the better mix you get. When you make a small batch a small difference in quantities of the two solutions results in a greater percentage difference and some times a batch might turn out gooey instead of hardening up properly.
To keep from wasting too much epoxy I use a syringe for precise distribution of the two solutions. I remove the needle portion of the syringe, fill them up from the epoxy tubes and use brass caps I made to seal them off. This makes it easy to distribute a very small amount on a surface to mix and get a good blend.