Why are blueprints blue?
The name stems from one of the first practical methods of copying images without simply tracing them by hand. John Herschel invented a way to do it with chemicals in 1842, and the process (called cyanotype) involved turning the paper blue.
You would do your drawing on a very thin piece of cloth or paper and lay it over a piece of regular paper that had been soaked in the key chemicals. Then, after being exposed to bright light, the paper would turn blue—except where the drawing was blocking the light from getting to the paper, leaving those lines white.
The process was extremely popular until Xerographic copies and computers started to take over, but the name stuck. Now, many blueprints are blue in name only.
Today, when I think about blueprint printing, it is said that the cost of this kind of drawing is lower than that of direct printing, and the storage time is longer. But now we use CAD. The electronic files are kept longer and the cost is not high. I searched the Internet to find out. Whether there is such a practice in the developed countries of formal enterprises and the machinery industry.
Why are engineering drawings and mechanical drawings blue? You may know that the word blueprint comes from this. I didn't know why the drawings should be blue before. I couldn't restrain my curiosity. I need to know.
In fact, the reason why these drawings are blue is related to their drawing methods. These drawings are not drawn or printed, but "sun-dried". Maybe in the streets, there are always some signboards like sun print pasted on the door of the printing agency, which refers to this.
The drawing was originally drawn on sulfuric acid paper, which is a kind of translucent paper. When drawing, a needle pen and ink should be used. Of course, many of them don't need to use a needle pen to draw, because CAD can directly draw and print on sulfuric acid paper. But when we went to school, we learned how to use a needle pen to draw on sulfuric acid paper. It seems that we want students to retain some basic skills. But to be honest, my pen has been used so many times. What I drew are the drawings that I handed in my homework. Maybe the course won't exist in the future.
The drawings drawn on sulfuric acid paper can't be used directly because it's very thin and easy to break. He is just the base map, with which many copies can be made.
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It’s because of how those documents are made. The blueprinting process was developed in the mid-1800s, when scientists discovered that ammonium iron citrate and potassium ferrocyanide created a photosensitive solution that could be used for reproducing documents.
The process goes like this: Someone creates a drawing on translucent tracing paper or cloth. The drawing is placed over a piece of blueprinting paper, which has been coated with a mix of ammonium iron citrate and potassium ferrocyanide from an aqueous solution and dried. When the two papers are exposed to a bright light, the two chemicals react to form an insoluble blue compound called blue ferric ferrocyanide (also known as Prussian Blue), except where the blueprinting paper was covered, and the light blocked, by the lines of the original drawing. After the paper is washed and dried to keep those lines from exposing, you’re left with a negative image of white (or whatever color the blueprint paper originally was) against a dark blue background.
When the two papers are exposed to a bright light, the two chemicals react to form an insoluble blue compound called blue ferric ferrocyanide (also known as Prussian Blue), except where the blueprinting paper was covered, and the light blocked, by the lines of the original drawing.
Ammonia printers, large-format copy machines that were around before toner was a thing. Ammonia prints are characteristically blue.
The term "blueprint" was originally derived from the visual aspects
of prints made using the contact printing process of cyanotype. The
blueprint process was invented as a cheap way to reproduce large
drawings. Special salts used in the process turn the paper blue.