Building a volcano using salt dough is a good classroom project. It's also an absorbing school holiday activity on a rainy day. Children can choose to build a realistic volcano, perhaps to add to a landscape display, or they could build one that will actually erupt. The dry, non-erupting volcano will last for years, but the salt dough will eventually collapse if it continually gets wet. Adult assistance will be necessary to take care of the baking process.
Things you need
Gather your volcano-making supplies:
Plain flour Salt Water Roasting tin Aluminium foil 500 ml plastic bottle Oven Acrylic paint and brushes 1 tsp washing-up liquid 2 tbsp bicarbonate of soda Vinegar
Make the salt dough
Make up a quantity of salt dough by mixing the flour and salt in the ratio of 2 tbsp flour to 1 tbsp salt. Add cold water gradually until the right consistency is reached. It shouldn't be too dry or too soft and floppy. The amount you need depends how big you want your volcano to be. Start with 14 tbsp flour and 7 tbsp salt. If you need more, make an additional batch.
Building the volcano
Place the bottle in the middle of the roasting tin. Crumple the tin foil around the bottle to make a volcano shape. Make sure you can remove the bottle easily, but leave it in place for now to provide a firm structure. Smooth the salt dough over the sides of the foil volcano. It should be roughly 2 cm thick. Spread the dough down and around the base, on to the roasting tin. Don't allow it to become too thin. Remove the bottle and carefully smooth the top edge of the volcano, making sure you will be able to replace the bottle after baking.
Drying the volcano
Place the roasting tin in the oven. Bake at 150 C or gas Mark 2. This a drying process, rather than cooking, so will take several hours. Check every hour, then more frequently as the dough hardens. It should deepen in colour very slightly and be firm to the touch. If the dough feels springy, it isn't done. Remove from the oven and allow to cool completely. Leave the volcano on the roasting tin if you intend to make the erupting version, otherwise you can carefully lift it off and place on a table or work surface.
Paint the volcano realistically, with green and brown sides until about half way up. Add red “lava” spilling over the top and downwards. At this point the non-erupting volcano is complete.
Replace the bottle inside the volcano and fill to within 5 cms of the bottle top. Add the washing-up liquid and bicarbonate of soda. Carefully pour in a little vinegar and watch the volcano erupt. The baking tin will catch the “lava”. Clean up and dry as best you can and the volcano will live to erupt again.
Additional tips: Repair any cracks that appear after baking with PVA glue. You could add red food colouring to the water in the bottle when making the erupting version. Give the non-erupting version a coat or two of interior wood varnish to preserve it for many years.