Why blueprints are blue

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Blueprints really were blue. In 1842 the astronomer Sir John Herschel found a way to copy drawings with sunlight: paper brushed with two iron chemicals turns Prussian blue wherever light hits it, and stays white under the lines of a drawing laid on top. Rinse it in water and you have white lines on blue. A year later Anna Atkins used the same process for the first book illustrated with photographs, and engineers and architects later copied ships, bridges and engines the same way. For more facts like this, and to learn how engineering drawings work, visit mach9.company. More products like this one in our shop: mach9.company/shop Beyond the Horizon. #blueprint #engineering #history #cyanotype