Fog-emitting machines are available on the market to create a light mist for everything from amateur film projects to neighborhood haunted houses. The mist created by the evaporating solution can create a spooky atmosphere, serve as a backdrop for a projector, or conceal elements of the environment. The solution is a very simple mixture of glycerine-based compounds and distilled water which, if done carefully and safely, can be replicated at home.
Fog machines or "glycol foggers" heat a water-based solution in an internal chamber. This vaporizes the compound and produces a fog, the density of which is dependent upon the concentration of the solutions. These devices are primarily rated by the power of their heaters, ranging from several hundred up to 1,000 watts. Higher-wattage foggers feature more powerful heaters, allowing them to better keep the "heat exchanger" chamber hot and ready to vaporize fog solution. Another way that glycol foggers are rated is by the volume of fog that they generate in cubic feet per minute (CFM). Different companies measure this in different ways, however, so it is not a reliable substitute for hands-on testing and comparison.
Homemade fog solution is made by first distilling and purifying an amount of water proportional to the amount of fog desired, depending on the rate that the machine evaporates the solution. The use of distilled water is necessary, as ordinary tap water will leave mineral deposits within the inner workings of the machine and cause it to clog. Next, a certain amount of commercially available glycerin (sometimes referred to as glycol), obtained from a drugstore, is stirred into and dissolved within the water. While many commercial for solutions also utilize one or more glycol derivatives in addition to this mixture, it is enough for most home or amateur purposes to produce an aesthetically-pleasing fog.
The amount of glycerin present in the solution can be altered in order to adjust the density of the fog that the machine will generate. A general rule agreed upon by hobbyists is a ratio of 1 part glycol to 8 parts water. In English units, this would result in a solution of 4 oz. of glycerin per quart of distilled water. For heavier fog clouds and mists, the ratio may be increased up to 1 part glycol to 4 parts water. This would yield a solution of 8 oz. glycerin in a quart of distilled water. When possible, the least amount of glycerin that will produce a desirable result should be used to minimize exposure to toxic chemicals.
To lesson the risk of glycerin poisoning, only use food-grade glycols. Fogging solutions and their by-products are toxic in large doses and many of them are also flammable. Thus, the chemicals must be kept out of reach of children and pets. If a spill occurs, clean and dispose of the substances carefully and thoroughly, and do not allow pets to lick up spilled chemicals. The fog produced by both homemade and commercially-made solutions can be irritating, especially to those with sensitive respiratory systems and allergies, so the machine should never be operated in an enclosed space. Read the fogger's manufacturer's guide to match the proper mix of chemicals to the machine's settings to prevent malfunctions. Be aware that using homemade solutions may also void the device's warranty.
- Comstock/Comstock/Getty Images