Why are blueprints blue? - Big Questions - (Ep. 206) | Mental Floss

Hi, I'm Craig. I'm an ex-Blue Man. Not part of the group. I was just a man who was blue

And this is Mental Floss on YouTube. Today I'm going to answer David Lev's big question

Why are blueprints blue? Nowadays, blueprint refers to any sort of plan, whether it's blue or not

But originally, blueprints had to be that color because they were copies that could only be made in blue

Let's get started. Or did we just answer the question? Let's get started. The process of making copies may seem simple now, but architects used to have to do it by hand, tracing copies whenever they needed one

Experts estimate that the invention of blueprints reduced the cost of copies to one-tenth of what it originally was

And you didn't have to friggin', you know, just draw all the time

Blueprints were invented in the mid-19th century. People needed a better way to reproduce plans for architecture and other projects

And some scientists found that a combination of ammonium iron citrate and potassium ferricyanide

created a solution that could help with this. How did they find that out

They're just throwing together, oh, what about this ammonium iron citrate and this potassium ferricyanide

Woo blueprints Scientists are amazing So to make a blueprint you coat a sheet of paper with that solution and allow it to dry Then you make the original plan on cloth or tracing paper You place a sheet on top of the paper that will be blueprinted then shine a bright light onto both and that

when the solution of ammonium iron citrate and potassium ferric cyanide do their thing

And by do their thing I mean they create a new compound, blue ferric ferric cyanide. The reaction turns the paper blue, and the lines on the original plan have blocked the

bright light so the blueprint stays white where those lines are. Basically, a blueprint

is a negative, and the reason that blueprints are blue is because the chemical reaction doesn't allow another color or even shades

Of course nowadays it's pretty easy to use a photocopier, a technology invented in the

30s that became mainstream in the 60s. But it took architects and engineers a while to switch away from blueprinting

In fact, the majority of those two fields turned to photocopies during the early 2000s

And if architects or engineers want a blueprint-like copy nowadays, they tend to create a white

print instead. It's basically the opposite of a blueprint, white paper with blue lines

White prints require diozonium salt and ozodye, which are less toxic than the chemicals used

in blueprinting. I wouldn't drink them though. Thanks for watching Mental Floss on YouTube made with the help of all of these nice diozonium salts

If you have a big question of your own that you'd like answered, leave it below in the comments. See you next week