To create a Watermark on a sheet of paper.
A watermark is an invisible mark on a sheet of paper for identification purposes. The watermark becomes visible when the paper is immersed in water. They are made by applying pressure that alters the fibers in the sheet of paper. This changes the reflection of light when the sheet is wet and hence the watermark becomes visible. They can also be used to write secret messages on sheets of paper. To do this, place a sheet of blank paper in water. Then put it on a glass pane and over it place a dry sheet of paper. Then write on the dry sheet, using a pencil. Remove the dry sheet and the writing will be clearly seen on the wet sheet. When the paper dries the writing will disappear, but will again reappear when the sheet is placed in water.