Smoking and foaming pumpkin

by Fellowship Agency October 20, 2017

Get ready for Halloween with this spooktacular #WhatsInMyTray demonstration.

Learning outcomes

You will be able to:

  • Describe the reaction of dry ice with air, water and soap solution.
  • Provide an example of a substance that sublimates.
  • Design and create your own Halloween pumpkin.
  • Outline the origins and history of Halloween and describe how this has led to our current traditions (in an age appropriate way).

You will need:


Take a look at our Smoking and Foaming Pumpkin video here for inspiration and read the ‘’What is happening?’ section to learn about the history and origins of Halloween and pumpkin carving.

What to do:

  • Carve your pumpkin into your chosen spooky design. See our handy pumpkin carving guide for help.
  • Place the pumpkin into the black shallow tray and surround it with an assortment of Halloween themed props (optional).
  • Set up your video recording equipment to capture the action (optional).

Demo 1

  • Lift the lid off the pumpkin and pour approximately 100ml of warm washing up liquid solution in to the hollowed-out centre.
  • Add approximately the same volume of dry ice to the liquid in the pumpkin and stand well back.
  • Spooky fog and foam will ooze out of the pumpkins mouth, nose and eyes.

Demo 2

  • Lift the lid off the pumpkin and pour approximately 100ml of warm water in to the hollowed-out centre.
  • Add approximately the same volume of dry ice to the liquid in the pumpkin, replace the lid and stand well back.
  • Spooky fog will gently flow out of the pumpkins mouth, nose and eyes.

What is happening?

The History and Origins of Halloween

Halloween is a festival celebrated in several countries across the world on the 31st of October. A shortened version of All Hallows Eve or All Hallows’ Evening, Halloween is thought to have originated from an ancient Celtic festival called Samhain (Summer’s end), which celebrated the end of the harvest season in Gaelic culture. During Samhain, pagans checked their food stores and prepared for winter. Celts from Britain and Ireland celebrated the start of their new year, All Souls Day or All Hallows’ Day, on the 1st of November. This date marked the end of summer and harvest time and the start of winter. It was believed that on the 31st October the world of the living and the dead overlapped before the start of the new year. The Celts believed that on All Hallows Eve, ghosts of the dead could return and destroy the harvest and food stores. To prevent this from happening, they lit bonfires on hill tops to ward off the evil spirits and protect their winter stores. For Christians, this was the start of a three-day observance of Allhallowtide, during which the dead, saints (hallows), martys and the faithful departed were remembered. Even now, modern Christians may attend church to light candles to remember departed relatives on the 31st October.

To ward off the evil spirits, Irish Celts would carve scary faces into turnips or mangelwurzel, this evolved into pumpkin carving in America because pumpkins are plentiful around Halloween and easier to carve. The hollowed-out vegetables are lit with torches or candles, they are said to represent either spirits or supernatural beings or used to ward off evil spirits. In America, Halloween Pumpkins are known as Jack-o’-lanterns. The name Jack-o’-lantern is thought to be related to will-o’-the-wisp, a visual phenomenon meaning ‘foolish fire’, where wisp means a bundle of sticks or paper sometimes used as a torch.

The Dry Ice Reaction

Dry ice is a solid form of Carbon Dioxide (CO2), it is very cold, less than -70 degrees Celsius. At room temperature, it slowly sublimes (turns directly from a solid to a gas) and is visible as fog/smoke. If dry ice is placed into a pumpkin on its own it sublimes relatively slowly. Gaseous CO2 is released and fills up the pumpkin, fog will escape from any holes.

Adding warm water speeds up this reaction, gas is released more rapidly, the pumpkin fills more quickly and fog spills rapidly from the pumpkin. Why does warm water speed up the rate of reaction? Warm water increases the amount of energy available to the reaction and causes the dry ice to sublime more quickly. What happens if you use cold water instead?

Adding washing up liquid solution results in the gaseous CO2 released on sublimation becoming trapped inside the bubbles, the pumpkin fills up with gas and bubbles until there is no more space and they are forced out of the top, mouth, nose and eyes. As the bubbles burst, or if you pop them, you will see clouds of gas being released.

Other things to try…

  • Try carving new and different designs into a pumpkin to funnel the fog and foam.
  • Try other carving other vegetables, such as turnips.
  • Does warm water or cold water result in the most spectacular reaction?
  • Is it possible to colour the bubbles to make them even more spooky?
  • If you have spare dry ice and would like to investigate it further, have a go at our exploding zip lock bags What’s In My Tray activity. <hyperlink to activity page>
  • Share videos of your spooky Halloween Pumpkin demonstrations on social media using #WhatsInMyTray. Can you make some spooky music to accompany your video?

Health & Safety

As with all Gratnells Learning Rooms What’s In My Tray activities, you should carry out your own risk assessment prior to undertaking any of the activities or demonstrations. In particular, take care when using dry ice, consult the relevant CLEAPSS guide, wear appropriate personal protective equipment and ensure adequate ventilation to prevent unsafe build-up of CO2.