I am using plate, window or bottle glass for each of the dragonflies and will be adding special frits or enamels to bring additional colors and dimension to each cast piece. I have been working on a 16-17 inch test size for the large dragonfly and it looks about half of them will weigh over 10 lbs and require over 2 and 1/2 days of kiln firing, annealing and controlled cooling.
Process-wise, I first make a 3-D model of the dragonfly in clay and then build a dam (using clay or other materials) around it and pour a plaster and silica mix on top of it. After this plaster/silica mix sets, I carefully dig out the clay which can be reused. After cleaning the mold, I then have a final mold to place the broken glass pieces into for firing. After cooling, the mold is broken away from the cast dragonfly. Additional coldworking with sanders, dremel bits, etc. is done to further clean and refine the glass casting. So, it is important to note that each dragonfly is cast in a one time use original mold and the mold is not reused since it must be broken to remove the cast dragonfly. The molds are about 20 inches across and weigh over 35 lbs.
The photos below demonstrate this process.
Clay model of dragonfly