Candy glass, also known as sugar glass, is a mixture of sugar, water, and corn syrup that can be used to simulate glass in movies, photographs, and plays. Although it is much less likely to cause injuries than real glass, it breaks convincingly, making it an excellent choice for stunts. Since candy glass is edible, it is also used to decorate desserts or eaten on its own. In this case, coloring and flavoring agents are generally used.
Combine sugar, corn syrup, and water in a medium saucepan, stirring thoroughly. Attach the candy thermometer to the side of the pan, making sure that the tip is deeply submerged but does not touch the bottom of the pan.
Heat the mixture over medium-high heat. Stirring is not necessary. Wait for the candy thermometer to reach 290 - 300 degrees, which is the hard crack stage.
While you are waiting, spray the cookie sheet lightly with non-stick spray, or apply a very thin layer of oil or shortening. If you are using oil or shortening, put about 1 tsp. directly on the cookie sheet, then use a paper towel to spread it evenly on the cookie sheet.
Quickly stir in the food coloring and flavoring extract, if you are using them, without removing the pan from the heat first.
Immediately pour onto the greased cookie sheet. Allow to stand at room temperature until completely hardened.
Cut or break into desired sizes and shapes. For decorating desserts, you can drop the cookie sheet onto the floor from waist height to create shards. You may want to cover the floor in the area with waxed paper to keep your floor and the candy clean.
If you are using the candy glass for a prop, you may want to sprinkle a very small amount of salt into the mixture while it is cooking. This will help prevent the "glass" from looking unrealistically shiny.
Do not attempt to speed up the hardening process by placing the candy glass in the freezer or refrigerator. This could cause it to shatter suddenly, sending pieces of the hardened "glass" flying. The heated sugar mixture is extremely hot and will stick to skin if spilled. Always use hand protection and exercise caution when dealing with heated sugar syrup. Even though candy glass is much safer than real glass, it can still cause injuries, especially when used for stunts.