First, we had to make the mountain. I took a plastic bottle and cut it down. We then made home made play dough out of a mixture of salt, flour and water. The ratio of flour to salt is 2 to 1 and I've found that water needs vary. I just add enough water until the consistency is correct.
I put a mixture of water, baking soda and a drop of soap into the bottle- and food coloring. We built the volcano around the bottle and then painted it. Without waiting for anything to dry, we added the vinegar (several times!). It was great fun.