What special ingredient was in the wardens nail polish book Holes by Louis Sachar?

There is no mention of any special ingredient in the warden's nail polish in the book "Holes" by Louis Sachar.

The warden is known for her strictness, her obsession with digging holes, and her love of her "special" nail polish, but the book never reveals what makes it special.

Perhaps you are thinking of a different detail from the book?