Writing in Fire
The following piece of chemical magic is rather interesting. Take a thin sheet of paper, about the size of this page, and draw or write on it a simple design, taking care to note that the lines of the drawing are continuous; that is to say, they must follow on. For ink, use a strong solution of nitrate of potash. This is invisible, and the picture will not be apparent when dry.
The next thing is to fold an edging of the paper, a quarter of an inch all round, so that the major part of the sheet is raised above the level of its support. Take a piece of string, light one end, then put out the flame and, with the smouldering tip, touch a spot where the ink is. The paper will burn along the course of the link and bring into view the design or writing which you drew, leaving the rest of the sheet untouched.
Your friends will like this experiment, especially if you have prepared sheets bearing their names.