![]() By the later 1890s in American architectural offices, a blueprint was one-tenth the cost of a hand-traced reproduction. Introduction of the blueprint process eliminated the expense of photolithographic reproduction or of hand-tracing of original drawings. the history of alterations recorded on the sheet.a record of the approved specifications.The result is a copy of the original image with the clear background area rendered dark blue and the image reproduced as a white line. The unconverted coating is washed away, and the paper is then dried. When a strong image is seen the frame is brought indoors to stop the process. Where the India ink blocks the ultra-violet light the coating does not convert and remains soluble. Where ultra-violet light is transmitted through the tracing paper, the light-sensitive coating converts to a stable blue or black dye. The frame is put out into daylight, requiring a minute or two under a bright sun, or about ten minutes under an overcast sky to complete the exposure. The tracing paper drawing is placed on top of the sensitized paper, and both are clamped under glass, in a daylight exposure frame, which is similar to a picture frame. Engineers and architects drew their designs on cartridge paper these were then traced on to tracing paper using India ink for reproduction whenever needed. This is a simple process for the reproduction of any light transmitting document. Excess ammonium ferric citrate and potassium ferricyanide are then washed away. ![]() The image is then developed using a solution of potassium ferricyanide forming insoluble ferroferricyanide ( Prussian blue or Turnbull's blue) with the divalent iron. When the paper is illuminated, a photoreaction turns the trivalent ferric iron into divalent ferrous iron. The paper is impregnated with a solution of ammonium ferric citrate and dried. The best known is a process using ammonium ferric citrate and potassium ferricyanide. The blueprint process is based on a photosensitive ferric compound. The blueprint process Architectural drawing, 1902 Architectural drawing, Canada, 1936 Practising engineers, architects, and drafters often call them "drawings", “prints”, or “plans”. The term blueprint continues to be used less formally to refer to any floor plan (and even less formally, any type of plan). It has almost entirely been replaced with digital computer-aided construction drawings. It was first largely displaced by the diazo whiteprint process, and later by large-format xerographic photocopiers. The process was not able to reproduce color or shades of grey. ![]() The blueprint process was characterized by white lines on a blue background, a negative of the original. It was widely used for over a century for the reproduction of specification drawings used in construction and industry. Introduced by Sir John Herschel in 1842, the process allowed rapid and accurate production of an unlimited number of copies. Compared to the cost of creating a large-format copying machine, a diazotype machine is a great bargain.A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets. The reason people still use blueprints is because it is an inexpensive process. This diazotype method produces dark lines on a white background, and is the popular method used today for reproduction of large-format drawings. The chemicals on the paper acquire color only in the areas not exposed to light. Ammonia gas or solution is used as a developer after exposure - it neutralizes the acid and allows the remaining diazonium salt to combine with the reactant to create a blue dye. The semi-transparent original is placed on top of the sensitized paper, and a copy of the same size as the original is made by direct contact. In the diazotype method, the paper is light-sensitized with a mixture of a diazonium salt (used in the manufacture of dyes), a reactant, and an acid that keeps the diazonium salt and the reactant from reacting with each other. This produces a negative image, with the drawing appearing in white against a dark blue background. The exposed paper is then washed in water. ![]() Where the areas of the sensitized paper are not obscured by the drawing, the light makes the two chemicals react to form blue. The sensitized paper is then exposed to light. The drawing to be copied, drawn on translucent paper, is placed against paper sensitized with a mixture of ferric ammonium citrate and potassium ferricyanide. Blueprinting is the older method, invented in 1842. ![]()
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