Why are blueprints... blue?

Henry Belcaster
Henry Belcaster
3 min read

Morning Blue Man!


You bang on that drum, Durd.

At risk of stating the obvious, you’re a really blue man dude.

Just like these super famous blueprints.

Here’s the first airplane:

And Ford’s motor vehicle:

And a super early architectural drawing:

So naturally you must be wondering why are blueprints…blue?

Well it started in 1840.

If you wanted to make a copy of something, you literally had to redraw or repaint whatever it was from scratch:

Ya that really sucked.

So this dude John Herschel gets tinkering in his lab.

So he starts combining chemicals.

Then soaking paper in them.

He had created a cyanotype! The world’s first blueprint.

So how’s it work?

Well basically you take your original drawing:

Place it on top of a piece of paper soaked in potassium ferrocyanide and ammonium citrate.

When you place them under UV light – like the sun – the bottom paper that’s soaked in chemicals starts to turn blue!

Aka blue ferric ferrocyanide.

And look really close.

Anywhere there was a black line in the original drawing, UV rays were blocked from hitting the chemical paper:

Lines don’t turn blue, they stay white.

You’ve made a copy!

Today we can just print stuff infinitely, but the term blueprint and that classic blue color stuck around.

Stay Cute,
Henry & Dylan 🌈

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