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The ferric salts are chemically altered when exposed to light. The exposed print is rinsed in water in order to release the organic acid in the coating.

A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets. Introduced by Sir John Herschel in 1842, the process allowed rapid and accurate production of an unlimited number of copies.

A blueprint's signature hue is tied to a chemical process. In 1842, an English photographer, chemist and astronomer named John Herschel discovered that combining ferric ammonium citrate and potassium ferricyanide created a chemical reaction and a compound called blue ferric ferrocyanide (or Prussian blue).

A drawing is made on tracing paper and then pressed against a chemical-coated paper. The chemicals on that paper are a mixture of citrate and potassium. The chemical-coated paper was then exposed to light, which caused a reaction and made the chemicals turn the paper blue.

In this process, initially created just to transfer notes, two papers are exposed to a bright light, and the applied chemicals create a permanent blue compound, called blue ferric ferrocyanide, except for where the paper is covered or has lines drawn. As a result, a solid-blue document with white lines is created.

Vellum is what many know as traditional blueprint paper, and it is commonly used for architectural and engineering plans for black-and-white blueprints. It is also possible to print blueprints on Mylar paper, which is transparent or frosted, by using a laser process.

The blueprint process was characterized by white lines on a blue background, a negative of the original. The process was not able to reproduce color or shades of grey. The process is now obsolete. It was first largely displaced by the diazo whiteprint process, and later by large-format xerographic photocopiers.

The color of blueprint paper changes to blue on exposure to UV light due to the formation of Prussian blue by the reaction of the iron salt and potassium ferricyanide.

The ferric salts are chemically altered when exposed to light. The exposed print is rinsed in water in order to release the organic acid in the coating.

A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets. Introduced by Sir John Herschel in 1842, the process allowed rapid and accurate production of an unlimited number of copies.

A blueprint's signature hue is tied to a chemical process. In 1842, an English photographer, chemist and astronomer named John Herschel discovered that combining ferric ammonium citrate and potassium ferricyanide created a chemical reaction and a compound called blue ferric ferrocyanide (or Prussian blue).

A drawing is made on tracing paper and then pressed against a chemical-coated paper. The chemicals on that paper are a mixture of citrate and potassium. The chemical-coated paper was then exposed to light, which caused a reaction and made the chemicals turn the paper blue.

In this process, initially created just to transfer notes, two papers are exposed to a bright light, and the applied chemicals create a permanent blue compound, called blue ferric ferrocyanide, except for where the paper is covered or has lines drawn. As a result, a solid-blue document with white lines is created.

Vellum is what many know as traditional blueprint paper, and it is commonly used for architectural and engineering plans for black-and-white blueprints. It is also possible to print blueprints on Mylar paper, which is transparent or frosted, by using a laser process.

The blueprint process was characterized by white lines on a blue background, a negative of the original. The process was not able to reproduce color or shades of grey. The process is now obsolete. It was first largely displaced by the diazo whiteprint process, and later by large-format xerographic photocopiers.