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<h1><center><em>Engineers and Architects use and create plans known as blueprints when they are normally just drawings on white paper, so why is that?</center></em></h1>
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<h3>In 1861 a French chemist discovered that ferro-gallate was light sensitive. Other scientists later found that an ammonium iron citrate and potassium ferrocyanide solution reacts the same way. When paper is coated with these substances, dried, and then exposed to light, the paper turns blue.</h3> 

<h3>The advantage of this process was soon evident in being able to quickly reproduce documents. </h3>

<h3>The image that is to be copied is drawn onto translucent tracing paper with a dark India ink. That tracing paper is secured over paper prepared with the photosensitive solution and exposed to UV light for a few minutes. When complete, it is taken out of the light and you have a blue document except where the dark lines of ink blocked the sun, those remain the color of the paper (usually white). </h3>

<h3>To stop any future UV light from changing the remaining un-blued lines, the solution is washed off the paper, which is then allowed to dry. This process also makes it very difficult to alter the document, usually a good thing.</h3>

<h3>This process was about 90% cheaper and resulted in duplicates that were made much faster and contained less errors than hand copying everything. This enabled ‘blueprinting’ to become so widespread that the name for such a document remained even after the process fell from common use in the middle of the 20th century, although most in the industries just call such modern day copies  “prints” or “drawings”. </h3>
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<h1>Today they have become a sort of engineering art. I have found a small assortment of blueprints, some real - some created as artwork.</h1>
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<center>http://i.imgur.com/wYqHQZT.jpg</center><center><h1>1875 Colt Peacemaker</h1></center>
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<center>http://i.imgur.com/jyqvTXG.jpg</center><center><h1>Sydney Opera House</h1></center>
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<center>http://i.imgur.com/vsIYb7m.jpg</center><center><h1>Wright Brothers 1903 Flyer</h1></center>
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<center>http://i.imgur.com/63qvoId.jpg</center><center><h1>Chrysler Building</h1></center>
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<center>http://i.imgur.com/o5qAzCP.jpg</center><center><h1>German U-Boat</h1></center>
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<center>http://i.imgur.com/LIKYpIS.jpg</center><center><h1>Brooklyn Bridge</h1></center>
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<center>http://i.imgur.com/HGMBTso.jpg</center><center><h1>Ford Model-T</h1></center>
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<center>http://i.imgur.com/wIqDpVN.gif</center><center>http://i.imgur.com/0snvu6p.gif</center><center><h1>Titanic</h1></center>
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<h3>Sources:</h3>
* <a href="https://en.wikipedia.org/wiki/Blueprint">Blueprints</a>
* Blueprints: <a href="http://www.wright-brothers.org/Information_Desk/Help_with_Homework/Wright_Plans/Wright_Plans_images/1903_Flyer_Blueprints_Plate_1.jpg">1</a> <a href="http://www.v-aline.com/upload/organonarchitecture.co.nz/Not_PC/GOFF-Gutman002.jpg">2</a> <a href="http://www.architechgallery.com/arch_images/architech_images/carbide/elevations_1a.jpg">3</a> <a href="https://img0.etsystatic.com/050/0/10050586/il_fullxfull.661651530_kt2c.jpg">4</a> <a href="http://images.fineartamerica.com/images-medium-large-5/1875-colt-peacemaker-revolver-patent-blueprint-nikki-marie-smith.jpg">5</a> <a href="http://www.abratis.de/sources/pictures/pic/blue/boat.gif">6,7</a> <a href="http://silodrome.com/wp-content/uploads/2012/01/Ford-Model-T-Blueprint-Cyanotype.jpg">8</a> <a href="http://cdn.silodrome.com/wp-content/uploads/2015/08/German-UBoat-Submarine-Blueprints-Original.jpg">9</a> <a href="http://worshiphousemedia.s3.amazonaws.com/images/main/s/mm/bbm/mm/blueprint.jpg">10</a>