blueprint, white-on-blue photographic print, commonly of a working drawing used during building or manufacturing. The plan is first drawn to scale on a special paper or tracing cloth through which light can penetrate. The drawing is then placed over blueprint paper, prepared with a mixture of potassium ferricyanide and ammonium ferric citrate. When the attached drawing and the blueprint paper are exposed to a strong light, the unprotected ferric salt not lying beneath the lines of the drawing is changed to a ferrous salt that reacts with the ferricyanide to form Turnbull's blue. This blue is the background of the finished print. The ferric salt under the lines of the drawing, protected from the light, remains and is dissolved during the washing in water that follows exposure. As a result, the lines of the original drawing appear white in the finished blueprint.

A blueprint is a type of paper-based reproduction usually of a technical drawing, documenting an architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan.


The blueprint process is essentially the cyanotype process developed by the British astronomer and photographer Sir John Herschel in 1842. The photosensitive compound, a solution of ferric ammonium citrate and potassium ferricyanide, is coated onto paper. Areas of the compound exposed to strong light are converted to insoluble blue ferric ferrocyanide, or Prussian blue. The soluble chemicals are washed off with water leaving a light-stable print.

A similar process was used to produce printing proofs for offset printing.

Various base materials have been used for blueprints. Paper was a common choice; for more durable prints linen was sometimes used, but with time, the linen prints would shrink slightly. To combat this problem, printing on imitation vellum and, later, mylar was implemented.


For almost a century blueprint was the only low cost process available for copying drawings. Once invented, no technical development was required; the process was put to widespread use immediately, notably in shipbuilding and the manufacture of railway locomotives and rolling stock.

The coated material ready for use has a shelf life of two days. Every industrial area had one or two small independent suppliers who made blueprint coated materials to order. These suppliers also provided a copying service for small users.

The normal use was to have a wooden frame with a spring loaded back, similar to a picture frame with a glass front. The drawing would be traced in India ink on tracing paper or tracing cloth. Indoors, coated paper and tracing would be loaded into the frame which was then brought out to sunlight. Exposure time varied from less than a minute to about an hour (under an overcast sky). The operator could see the blue image appear through the tracing, when ready the frame was brought indoors. The material was washed in running water to remove the unexposed coating, then dried. It gave a clearly legible copy of the drawing with a white line on dark blue background. This copy possessed unlimited resistance to light and resistance to water that was as good as the substrate.

The diazo document copying process progressively took over from blueprint during the period 1935 to 1950.

Replacements for blueprints

Traditional blueprints have largely been replaced by more modern, less expensive printing methods and digital displays. In the early 1940s, cyanotype blueprint began to be supplanted by diazo prints or whiteprints, which have blue lines on a white background; thus these drawings are also called blue-lines or bluelines. Other comparable dye-based prints are known as blacklines.

Diazo prints remain in use in some applications but in many cases have been replaced by Xerographic print processes similar to standard copy machine technology using toner on bond paper. More recently, designs created using Computer-Aided Design techniques may be transferred as a digital file directly to a computer printer or plotter; in some applications paper is avoided altogether and work and analysis is done directly from digital displays.

As print and display technology has advanced, the traditional term "blueprint" has continued to be used informally to refer to each type of image.

Blueprint companies

Although the industry has converted to the whiteprinting system, the companies have primarily stayed the same. Among the largest as of 2006 is NRI, a ReproMAX founding partner, with eight offices in New York, Boston, Philadelphia and Washington, DC, and BP Independent Reprographics, which is the result of several mergers and buyouts between Independent Blueprinting, Crown Reproductions, and The Blueprint Company.

With the advent in large, conglomerate, corporate entities, it is becoming increasingly difficult to find the traditional, family-owned blueprint shop. Most small to medium-size "blueprinters" are now owned by much larger corporations like American Reprographics Company (they alone own over 235 print shops in the US and Canada).

However, there are still some truly independent shops. Among them are University Reprographics in Seattle, and Bill's Blueprint in Everett, Washington.

A similar network has been built up as a connection of independent reprographers, as members of ReproMAX. As a result, ReproMAX has grown to be the largest association of reprographics companies, with over 230 current network partners in North America and Western Europe. The electronic planroom and document management solution for ReproMAX is available as ReproMAX/DFS.


See also - The largest free blueprint collection on the net, with more than 25000 3-view drawings online.

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