Here's a list of other equipment you may find helpful: Glassine envelopes are made of a special thin, see-through paper that protects stamps from grease and air. You can use them to keep stamps until you put them in your album. A stamp catalog is a reference book with illustrations to help you identify stamps. It also lists the values of used and unused stamps. A magnifying glass helps you examine stamps by making them appear larger. A perforation gauge measures perforations along the edges of stamps. Sometimes the size and number of perforations (or "perfs") are needed to identify stamps. A watermark tray and watermark fluid help make watermarks on stamps more visible. A watermark is a design or pattern that is pressed into some stamp paper during manufacturing.