Blueprint
Why is it called that?
Sir John Herschel lived in Kent, England. He was a polymath who was a mathematician, astronomer and chemist.
He named 7 of Saturn’s moons and 4 of Uranus’, a planet discovered by his father Sir William Herschel. He is also known for advocating the inductive approach to scientific experimentation.
In 1842, he was experimenting with a few chemicals, specifically compounds of Iron. He intended to create a photochemical reaction that would reveal an invisible form of the infrared part of the spectrum that his father had detected.
He was particularly interested in photography. He came up with a process that used ultraviolet light using iron compounds.
Since the chemicals were iron-based, the print would be cyan-blue and hence they were known as Cyanotypes.
This process was first used to create pictures. Then it was discovered that the same process could be used to create copies.
An existing plan drawn on translucent tracing paper could be copied by placing it on top of another piece of paper coated with photosensitive chemicals and exposed to ultraviolet rays (sunlight).
The sheet coated with the chemicals would turn blue due to the reaction of the chemicals to the light. However, the light would not be able to penetrate the parts of the document where the lines were drawn and that part would remain white in the chemical-soaked sheet.
This technique was called the Cyanotype and since the resulting sheet was blue, it came to be known as a blueprint. It was often used to make copies of complicated plans and drawings that needed to be reproduced and shared.
Hence the word blueprint caught on.