I don't have any firework stamps, but I did find something else from the night sky in my stash - a star stamp. Embossed in silver and painted with mica powder these stars were perfect for the effect I was looking to create. You add a small amount of water into some powder and paint it on with a fine brush.
When it dries the pigment is fixed, so no smudgy messes.
I cut them out by hand and love the way they stand out on the black card stock, slightly curling in the points. The sentiment is from Merry and Type and I've added a double scored border.