Step 3: Make the fossil shells
Test that it's pliable enough to work by hand - roll a small ball between your palms - if it flakes or crumbles, soften the dough by working in a little more milk or water - just cut and mix it into the dough with a knife.
Take small pieces of dough and roll them into long, tapered cones.
Mark a series of evenly-spaced lines all the way along - either with the blunt side of a knife, or by rolling a small balloon whisk gently along.
Starting at the thin end, carefully coil up the dough into a spiral, then slice off the thick end square to make the shape of an Ammonite shell
Carefully transfer the shells to their places on the rolled-out slab - make an assortment of different sized shells (the larger ones fit into the circular depressions made earlier - the small ones can go straight on top) Roll some of them up the oposite way, for variety.