What exactly is a blueprint?
If you have ever watched a house being built, or if you have ever had an addition put onto an existing house, you know that the standard method of communication is a big piece of paper called a blueprint. Blueprinting is the standard method used to copy large architectural and construction drawings. A blueprint used to consist of white lines on a blue background. A more recent process uses blue lines on a white background. The term “blueprint” is usually used to describe two printing methods, the blueprint and the diazotype. Blueprinting is the older method, invented in 1842. The drawing to be copied, drawn on translucent paper, is placed against paper sensitized with a mixture of ferric ammonium citrate and potassium ferricyanide. The sensitized paper is then exposed to light. Where the areas of the sensitized paper are not obscured by the drawing, the light makes the two chemicals react to form blue. The exposed paper is then w
