Use the white wax crayon to draw a ghost on the white card: a large rounded dome head, a body narrowing gently at the waist and widening again at a wavy hem. Press firmly with the crayon so the wax is thick on the paper. Add two oval eyes and a small mouth. Draw a few dots and stars around the ghost if you like. The drawing is completely invisible on the white card at this stage.

Mix dark watercolour paint with water to a medium wash, not too diluted and not too dark: test it on a scrap of the same card first. You want it to be transparent enough to show contrast but dark enough to reveal the white wax clearly.

Brush the watercolour wash quickly and evenly over the entire card surface, working in one direction with the wide brush. Do not go back over an area you have already painted while it is wet: the wax will smear and the ghost edges will blur. One pass is enough.

Leave to dry flat for 10 minutes. The ghost will appear in crisp white against the dark background. Write a name or message on the reverse. These are most effective with a dark navy or charcoal wash rather than a pale one.