Sugar glass is, at its most basic, a molded lollipop. It is candy which has been molded to look like glass. It has been used in films, and theater for a very long time (in other words, I don't know exactly, but it's been a while). It is hard candy, but to get the right physical properties requires a little chemistry.
These days, fake break-away glass is now typically made from a clear resin, but for low-budget or home fun, you can make your own with just a few simple things.
Step 1: What You Need
- 1 C Water
- 1.75 C Sugar
- .5 C Corn Syrup - the clearer the better
- .25 t Cream of Tartar
- Sauce Pot
- Spoon or spatula (I recommend high temp silicone)
- Candy or Deep Fry thermometer (needs to go up to 300 degrees accurately)
- Corn Starch
Step 2: Sugar
Common table sugar is also called sucrose. It is a disaccharide (two sugars) of glucose and fructose, with the molecular formula C12H22O11.
The glucose and fructose are connected by a single oxygen atom. By applying heat and an acid (cream of tartar), you can break the bond between the saccharides. More on that later.
Sugar is hygroscopic which means that it really likes water. If you've ever left hard candy out in the open on a humid day, you've probably returned to a sticky mess later. Therefore, any sugar glass that you make, you need to use quickly.
In theory, you can make sugar glass with just sugar, water and heat, but it will be very unstable as you make it, and very likely to burn or flash crystalize.
See the following links on Sucrose for more information:
Step 3: Cream of Tartar and Corn Syrup (Chemical Voodoo)
You can omit the cream of tartar, but it has magical properties (well, OK, not *magical*... but it does help out quite a bit). Cream of Tartar, or Tartaric Acid is a biproduct of the wine making industry. It is known chemically as potassium hydrogen tartrate, and has a chemical formula of: KC4H5O6. Tartaric acid is also a primary ingredient in baking powder. So, if you ever run out of baking powder, just use equal parts of baking soda (a base), and cream of tartar (an acid).
As for the "magical" properties... it is used to prevent the sugar from crystalizing. It does this by breaking down some of the sugar molecules at the single oxygen atom, creating single molecules of glucose and fructose.
The corn syrup is mostly glucose, and acts as a buffer between sucrose molecules preventing them from joining together in one giant mass and ruining your crystal clear confection. Since we are using corn syrup, you can omit the cream of tartar, but I like to hedge my bets, and I've found that I get a better result more consistently (less likely to flash crystalize when the heat is off) when I use the cream of tartar.
Step 4: Making Candy
In the sauce pot, combine the water, sugar, corn syrup, and cream of tartar. Stir to dissolve as best as you can. The heat will finish dissolving it. Turn the heat on high and let it come to a boil.
The process of making hard candy is really just dissolving the sugar crystals in a medium (water), and getting rid of the water. The sugar is then one big crystal. If allowed to cool properly, it will be a semi-clear solid mass.
When the mixture comes to a boil, it is time to put in the candy thermometer. You are going for a hard-crack. This is about 302 degrees Farenheit (150 degrees Celsius). If you have never made candy before, or are unfamiliar with the candy stages... Before there were neat candy thermometers, cooks used to keep a cup of cold water near the pot to test the doneness of the mixture. A small bit was taken out of the mixture and dropped into the water. Depending on the reaction, it told the doneness level of the candy.
- Thread Stage - 215 F or 108 C - The candy forms very soft threads. This is used for syrups.
- Soft Ball - 235 F or 118 C - The candy forms a soft maliable ball, but will flatten by itself. Fudge is a soft ball candy.
- Hard Ball - 250 F or 125 C - The candy forms a firm ball that will not flatten by itself, but will squish if pressed between the fingers. Caramels are a good example.
- Soft Crack - 270 F or 135 C - Candy dropped into the water will form pliable threads that will bend before they break. Taffy is a soft crack candy.
- Hard Crack - 300 F or 150 C - When dropped into the water, you will hear a noticable "crack" sound. Hard Candies, and sugar glass.
The temerature is a bit flexible, so you don't have to be that precise. I usually stop cooking a hard crack at 302 degrees, and it will get up to about 307 degrees with the carry over heat.
The temperature will rise slowly as the water boils out. As the mixture becomes more and more concentrated, it becomes less stable. Remember, the water is the only this that was keeping the sugar from recrystalizing. Be careful of the crystals on the side of the pot falling into the mixture. If the sugar gets a crystal in it, it will recrystalize in a flash, the only thing you can do at that point is add more water and start over. The corn syrup (pure fructose) and the cream of tartar (an acid to break down some of the sugar) will help you avoid that messy possibility, but it is still a possibility.
When the temp reaches 302 degrees F, remove it from the heat, and set it aside to cool a bit before working with it. This will also help get some of the air bubbles out. This is a good time to remove the candy thermometer.
Now, here is the most important warning: Professional chefs call this stuff culinary napalm! It is 300 degrees, and it sticks to everything. It is a very good way to get a very nasty burn. Please exercise caution when dealing with this stuff. I take no responsibility for your actions.
Step 5: Mold Prep
I won't go into making custom molds, I recommend the following instructable for that:
However, I do recommend using food grade silicone, as it can deal with the heat, and won't leave any nasty residue should you decide to eat your creation.
Coat the inside of the mold with either a light cooking spray (not recommended) or a light dusting of corn starch. The corn starch will also help keep the item dry longer.
Step 6: Making the <Insert Your Application Here>
Pour it into the mold. I made a bottle mold for mine, so I pour mine in and then keep rotating the mold until the sugar is set enough that I can put it down. Let the item cool completely, don't jostle it, don't get it wet, and don't unmold it before it's done!
Step 7: Other Applications
Breaking stuff without the mess - I let my wife break a sugar glass bottle over my head. It was very theraputic for her.
Runner Up in the
Hungry Scientist Contest