Why is a blueprint called a blueprint?

Question

My 5 year old son asked me.

Answer 1

i'm no engineer but original blueprints were printed in blue ink, that's where i thought it came from

Answer 2

The process they used many years ago to make copies of a drawing resulted in a sheet that was blue in color, with the lines being white. A negative if you will of the original drawing. This was the reason blueprints are called blueprints.

Answer 3

Hello pdgr2000 & son -

Well the term "blueprint" stuck as meaning the original plan for things, as in the 1930's to 1960's, large copies or technical drawings etc. were really only re-producable by shining an ultra violet light onto photo-sensitve paper, which starts off as yellow, with a translucent film in the way with all the details.
Then "developed" using ammonia. An alarming stink in the print room !
The result was blue paper with white lines, as per the original.

Literally a blue print of the item.

Thankfully, we have better copying methods now, but calling for the "blue-print" still has meaning, if referring to the original drawing

Hope that helps,

Bob.

Oh, PS. you can still get the paper, in light-proof bags, and put items such as leaves or whatever on top, left out in the sun to give yellow images, lthen "fixed" by brushing with diluted Domestos or similar. Nice effects, if a tad messy !
Wear gloves !

Answer 4

Good question! It's a historical term, which relates to the printing technology that was used to reproduce drawings. It had a dark blue ink, which meant that the image printed was in blue. Hence, the general term for a construction plan became "blueprint", which has stuck around longer than actual blueprinting machines have.

Answer 5

I don't think it was anything to do with the ink ! The paper is blue and the drawing is white.

The old way of copying large drawings was to create a photo image on paper or linen using ammonium (I think) to make the surface photosensitive.
The process called Cyanotype was very slow and it smelt very bad. The result was a negative "white on blue" image of the original "black on white". The paper was blue because of the ammonium.

Now we have photocopiers and printers than can print off large sheets very quickly (and even fold them!)

Regards

Stu

Answer 6

Strictly speaking they are not "prints", as they are not printed, they are copies.

In the "olden" days we did not have big photocopiers, so the next best thing was the process described by a previous answerer, which used special coated paper which was sensitive to ultra violet light, using ammonia to fix the image.

It was more like a photograph, but the impression left on the paper was only single colour, and that colour was blue.

Answer 7

blueprint is originally used in astronomy in the 19th century.the process involves a paper coated with photosensitive compund that consists of ammonium ferric citrate and potassium ferricyanide. When expose to strong light, ammonium ferric citrate and potassium ferricyanide reacted with each other producing an insoluble ferric ferrocyanide which is in blue in color. thats where they get the blueprint name.

p/s the process is somehow like etching process

Answer 8

All these people who think they know are absoloutly spot-on.

In the older days, plans were written (Printed) in Blue ink, hence the term "Blue-print"

Nowadays, blueprints come in other colours because of changes in printer technology.

BTW: The answer above, whilst correct, might not be best for a 5 year old, but you could if you want.

Answer 9

Decades ago they used a sort of photographic process to make copies of large engineering drawings. There was a yellow diazo dye coated on the paper. The dark line of the original prevented UV light from destroying the diazo dye. After this contact exposure the copy was in yellow, hard to see. Next ammonia vapor turned the diazo dye blue and pretty much locked it so it would not fade.

Answer 10

I thought it was because original blueprints are put on the robust blue paper stuff...