How color changed engineering graphics

How color changed engineering graphics

Today, drawings on monitors are full of dozens of shades, but a century ago, engineering was associated exclusively with deep blue. We recall how cyanotype appeared and why the legendary drawings are still called "bruises".

The birth of technology

Until the middle of the 19th century, drawings were reproduced manually: tracing paper was applied to the original and lines were drawn. It took hours and was fraught with errors. The revolution took place in 1842, when the British scientist John Herschel discovered the sensitivity of iron salts to ultraviolet light. This is how cyanotype was born, a silverless process that produces a stable monochrome image of saturated blue.

The principle of "blue"

The technology was ingeniously simple: the paper was impregnated with a chemical compound, a tracing paper with a drawing was placed on top and kept in the sun. Ultraviolet light turned the exposed areas blue due to the Prussian blue, and the lines covered with ink remained white. After rinsing with water, a clear negative was obtained — light lines on a bright blue background.

The era of industrialization

The peak of popularity occurred in the 1920s and 30s. During the construction of the Dneproges and Magnitogorsk, the speed and low cost of the Sinka became decisive factors. It was then that the term firmly entered the lexicon and became synonymous with a working drawing, replacing the concepts of technical specifications and design documentation.

Were there any other colors?

Later, the cyanotype was replaced by the diazotype, which made it possible to obtain positive copies (dark lines on a light background). However, the name "blue" has been preserved in Russia for decades. In the middle of the 20th century, watercolor washing was also used for educational purposes: the background was pink-lilac or yellowish, and carmine, sepia and emerald greens were used for coloring. We chose muted tones — they tired the eyes less and helped us perceive the shape more accurately.

Color in modern CAD systems

Today, there is no single color standard in engineering graphics. ESCD is focused on black and white graphics for clarity of contours. However, color is actively used for clarity: in assembly drawings, diagrams, and presentations. In the COMPASS and nanoCAD systems, color has become a practical tool: the main lines are blue, the thickened ones are turquoise, and the dimensional ones are black. When printing, the differences are preserved due to the thickness of the strokes.

The return of tradition

Interestingly, cyanotype is experiencing a renaissance today, but already in art. It is used for abstract compositions with plants and lace. Some architectural firms deliberately preserve blue prints as a symbol of the continuity of the profession, turning them into valuable artifacts of material culture.

Blue was the language of engineering, and its history goes from a solar workshop to digital screens.

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