You don't need to be a Hollywood special effects technician to learn how to make smoke come out of a cauldron without a fire. A bit of dry ice covered with water or a mini fog machine makes the cauldron in your Halloween haunted house or your next costume party boil over with a spooky smoke or fog that drifts along the floor.
When creating spooky, cool smoke, you have the option of using a battery-powered or electric fog machine. You can buy a mini fog machine for less than $50, at the time of publication, a good investment if you plan to use it every year. Fill the fog machine with the fog juice you need to get to make it work. Set it inside the cauldron and plug it in or turn it on. Small fog machines use about 1 quart of the liquid to create two hours of fog.
Dry Ice and Cauldron Size
Place the cauldron near a window to ensure some ventilation in the room. Use about 1/2 gallon of water to each pound of dry ice for the best results. If you add too much or too little water, it doesn't make as much cool smoke or create the desired foggy effect. Measure the thickness of the total amount of dry ice you plan to use and select a cauldron with a depth three times that measurement. This allows the smoke to puddle in the cauldron before spilling over its edges.
Send the Smoke Along the Floor
The smoke or fog created by dry ice or a fog machine disappears in just a few feet. To carry the effect throughout the room, set a small fan behind the cauldron – where it won't be seen – to help spread the smoke along the floor. When using dry ice, if the water becomes infused with too much of the carbon dioxide, the smoky or fog effects diminish significantly. Add fresh water periodically and replenish the dry ice as needed to keep the effect going.
How Dry Ice Works
As a solid mass of carbon dioxide, after you remove the packaging from dry ice – available at most grocery stores – set it carefully in an appropriately sized cauldron while wearing hand protection. When water is mixed with frozen carbon dioxide, a heavy vapor composed of water and the CO2 develops. Because the vapor is heavier than air, it pours over the sides of the container and hovers just above the floor.
Monitor Children and Pets
Do not leave dry ice in a cauldron unattended with children present. Store it in a loose-lidded ice chest or in the freezer until you need it. Do not leave it in a closed car or in an airtight container; when the dry ice turns to gas, it builds up pressure and can cause an airtight container to explode. Do not allow curious children to reach inside the cauldron. Dry ice is very cold – it freezes at -110 degrees Fahrenheit -- and can damage your skin if you even handle the package around it. Always handle it with thick, well-insulated gloves, or use tongs to pick it up.
Because dry ice is made of frozen carbon dioxide in a solid form, when mixed with water, it creates a heavy vapor. Keep small pets out of the room in which you use it, as it can suffocate them if they are on the floor. Ensure the room has adequate fresh air ventilation by cracking a window. Keep the CO2 in the freezer until you need it; as it melts, it turns into a gas and is no longer as effective in creating the vapor as when it is frozen.