Get several boxes of bathroom mirror tile from your local lumber yard.If you have a choice, get the thinner tiles to keep the weight of the dish down.
Wear eye and hand protection when cutting glass.
I built a simple cutting jig from some 1/4" plywood and scraps of pine.
The wood cutting jig is placed over the mirror tile, and with a sharp glass cutter, you scribe a line, remove the 1" spacer, and scribe again. The first spacer must be the glass cutters thickness thinner than the rest, which for my glass cutter was 7/8". When all the scribe lines are finished, wipe or blow off the glass surface to remove any chips of glass,then turn 90 degrees, and scribe from the other direction.
When all the scribe lines have been finished, apply downward pressure while placing the central scribe line over the edge, (***always break away from your face****), as tiny shards of broken glass can be produced and thrown in the direction of the break.Repeat until the pieces get small, then break them by hand.Each 12 " mirror will produce 144 1" mirrors. Apply a small dab of silicone to the mirror rear, and carefully stick to dish.Don't worry if some silicone pushes out between the cracks, as we will cut that off after the silicone has cured for several days.