OCR Text |
Show For Secret Writing ' T Most Invisible Inks are made with paste drier as a base and one of the mineral salts as a coloring medium. Heat Is used to develop the printing and moisture to make It disappear. Of the chemicals possessing this property are cobalt chloride, barium sulphate, barium nitrate, copper chloride, dilute sulphuric acid, potassium potas-sium nitrate, and equal parts of alum and garlic juice. Another form of Invisible ink Is made from a mixture of transparent tint base and paste drier. It 13 Invisible In-visible when dry, but shows up clearly clear-ly when rubbed with an ordinary lead pencil. . |