A while ago, I was given a photocopy of this great 'recipe' for air drying dough. It is easy to make and works out much cheaper than air drying clay (which is hard to get and expensive where we live).
You will need:
Half a cup of cornstarch / cornflour
One cup baking soda
Half a cup of cold water
Put the ingredients in a saucepan and stir over medium heat for a few minutes until the mixture thickens to look like moist mashed potatoes. Then place the mixture on a plate and cover with a damp cloth until cool. Knead it like dough. It is then ready to use.
I have found that it must all be used in one go - it goes hard within a day and is unusable.
The recipe that I was given had an example of using it to make fossils, so that is the first thing we did. We shaped the dough into balls which the boys then flattened out with the palm of their hand. Then they pressed shapes into it - shells, rocks, leaves, a toy lizard. I do not have a photo of these as they were taken out into the sandpit and garden and buried to find later as 'fossils' and who knows where they are now!
But we also used this dough to make these diya lamps.
The boys just made the basic shape, but Miss Butterfly made more elaborate shapes. She had also made a flower shaped one that was beautiful, but she dropped it while painting it.
This is a really versatile recipe and because the clay is white, painting shows up clearly and you don't need tons of paint to make the colour show up.