There are several late-1800 early-1900 opera related postcards that have very special attributes. Their image changes when held up to a bright light. These are called transparency or hold-to-light postcards and there is a difference between the two. The hold-to-light postcards generally contain cut-outs on the top layer of the postcard revealing another colored layer underneath that would be illuminated under light. Cut-out postcards allow for very specific areas to be illuminated. The transparency postcards do not have cut-outs. They have a separate image or plain colored tissue between the front and back layers of the postcard that illuminate under light. Today, because of their rarity, animation, and beauty they command a high price.