Play dough

At school we are doing a topic on dinosaurs, so I made some grey play dough to be rocks and the children made pretend fossil imprints of plants and dinosaur footprints. I have never made cooked play dough before.. it is certainly more like shop bought play dough and easy to make (although I got the husband to wash the pan for me). Here is the recipe:
Ingredients:
2 cups of plain flour
1 Tbsp. of cooking oil
1 tsp. cream of tartar
2 cups of coloured water
1 cup of salt
Directions:
Place all of the ingredients in a medium size or large pan. Cook slowly on medium-high and stir it until the play dough thickens. Keeps best in the fridge in plastic containers.

They really enjoyed pushing things in to it and it led to some great discussions about materials that would be good to leave imprints in (mud at a waterhole for example).  This followed on from reading this great book on how fossils are made:

Incidentally, I also fancy having a go at this cloud dough: http://www.flightsofwhimsy-ece.com/2011/10/playdough-no-cloud-dough/