History of Medicine
Technologies of Anatomical Representation
Woodcut: To make a woodcut, an engraver starts by drawing an image, usually a tracing of a pencil drawing, onto the side grain of a wood plank. Areas not printed are cut away well below the surface with a knife or gouge, leaving the flat surface to be inked. Woodcuts can be put into type blocks along with moveable type, so that the image and type can be printed together in one run through the press. [Introduced into Europe: 1300s.]
Copperplate engraving: In copperplate engraving, an engraver copies a drawing onto the surface of a copper plate. Areas that will be white when printed are cut away below the surface with a sharp tool, leaving the flat surface to be inked. Copperplate engravings allow for finer lines and more detail than woodcuts, but the printing of the image requires more pressure than type or woodcuts (leaving a characteristic line of indentation around the image). Because of this difference in pressure, if moveable type on the page is desired then the page has to be run through the press twice, once for the image and once for the type. [Invented: 1523.]
Hand coloring: Before the invention of multiple-layer color printing, printed black ink anatomical illustrations were sometimes colored freehand, or in some cases with a stencil, using tempera or watercolor.
Mezzotint: Unlike other engraving techniques, mezzotint proceeds from dark to light. A metal plate is totally abraded with a tool called a rocker. If inked and printed at this point, it produces an even, rich black. The design consists of areas of tone rather than lines, and is produced by smoothing areas of the plate with a scraper or a burnishing tool. The more scraping or burnishing, the lighter the area. The resultant illustrations have effects of light and shadow. By printing multiple color layers, different shades can be combined to produce rich hues that look much like oil painting. [Invented: 1642.]
Etching: In etching, a plate is covered with a thin, acid-impervious coating. Lines are drawn through the coating with a stylus, exposing the metal of the plate. An application of acid then eats into the exposed areas. The longer the plate is exposed to acid, the deeper the bite and stronger the line. An etching usually has a free and spontaneous appearance, with great delicacy of line, but can also mimic the formality of engraving. [Invented: 1630s.]
Wood engraving: In wood engraving, an engraver draws an image on polished blocks of dense end-grain wood (usually boxwood). Tools similar to metal engraving are used to produce non-printing lines. The uncut surface takes the ink and prints onto paper. The block can be inserted into a frame along with moveable type, and the entire page can be printed in one run through the press. The process allows for more detail than the older woodcut technique. [Invented: 1780s.]
Lithography: In lithography, a design is drawn or painted on a polished or grainy flat surface of a stone with a greasy crayon or ink. This image is chemically fixed on the stone with a weak solution of acid and gum arabic. The stone is flooded with water, which is absorbed everywhere except where repelled by the greasy ink. Oil-based printer’s ink is then rolled on the stone, which is repelled in turn by the water-soaked areas and accepted only by the drawn design. A piece of paper is laid on the stone and run through the press with light pressure. The design may be divided among several stones, properly registered, to produce a lithograph in more than one color through multiple printings on the same page. [Invented: 1798.]
Photography: Photography is a process invented in the 1830s and ‘40s in which an image is produced on a chemically sensitized surface by the action of light. Unlike previous processes of anatomical representation, the image created is a "copy" of the subject, produced by technology, not recreated by the hand of an artist. [Invented: 1830s.]
Relief halftone: Relief halftone is an industrial form of photo-etching. First the artwork is photographed through a dot screen. The negative is exposed onto a zinc plate covered with light-sensitive gelatin. The picture is now converted into a dot pattern. The gelatin on the zinc plate is sensitized by the light through the negative in the shape of the line drawing, and the gelatin which has not been sensitized is washed away. The sensitized area is then covered with a waxy substance resistant to acid; the rest of the plate is etched, so that the dot pattern appears in relief. The image then can be inked and printed onto paper. [Invented: 1880s.]
X-ray imaging: The X ray is a form of radiation produced by accelerating a flow of electrons through a vacuum tube. In 1895 Wilhelm Roentgen performed experiments showing that radiation emitted by this process could pass through flesh and other low-density substances that are opaque to ordinary light, but not bone. Roentgen discovered that X rays could produce viewable images of the interior of the body on a photographic plate or on a screen with a fluorescent coating ("fluoroscope"). [Invented: 1895.]
Digital imaging: Digitization is based on the idea that the continuous physical world of our experience can be divided into tiny pieces, and that these pieces can be measured and represented by a set of numbers. Color pictures can be digitized by measuring the color at closely spaced points (usually from 72 to 1200 dots per inch, or dpi). The color of each dot is then represented by three numbers indicating the combination of red, green, and blue that will reproduce the original color. Digital imaging is a powerful tool because numbers, unlike physical objects, can be reproduced perfectly, transmitted easily, and manipulated using computer programs.
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