A blueprint is a photographic print where solid forms and lines are drawn on a specially prepared blue background. In most cases, the background is in the form of a blue paper. The usage of the blueprint is to form an elaborate plan of action. If one wants to make an architectural plan, an engineering design or construct a building, one should have the plan on "paper" at first. The blue print serves as a prototype or model of the plan which is to be conceived.
To begin with, the plan is first conceived on a special paper through which light can enter. The drawing is then positioned over the blueprint paper, which is made of a mixture of ammonium ferric citrate and potassium ferricyanide. On exposure of the drawing and the blueprint paper to the sharp light, the ferric salt lying above the drawing reacts with ferricyanide to form the blue background of the completed print. After the exposure, the ferric salt lying below the lines and protected from the light is dissolved in water. Thus the lines of the drawing appear white eventually in the blueprint.
To begin with, the plan is first conceived on a special paper through which light can enter. The drawing is then positioned over the blueprint paper, which is made of a mixture of ammonium ferric citrate and potassium ferricyanide. On exposure of the drawing and the blueprint paper to the sharp light, the ferric salt lying above the drawing reacts with ferricyanide to form the blue background of the completed print. After the exposure, the ferric salt lying below the lines and protected from the light is dissolved in water. Thus the lines of the drawing appear white eventually in the blueprint.
