This exhibition includes works in a wide range of different media. Below is a brief guide to some of these techniques.
This process was the principal method of printing photographs from the 1850s until the end of the 19th century. Ordinary paper was coated with a layer of albumen (egg white) and salt, and then sensitised with a silver nitrate solution, to form photographic paper.
Bronze casting: the lost wax method
The piece to be cast in bronze is first modelled in wax. This is then surrounded with plaster or clay, leaving holes at the top and bottom, to make a mould. This mould is heated gently so that the wax melts out. The plaster or clay mould is then embedded in sand and the mould is filled with molten bronze through the hole in the top. When the metal is cool, the mould is chipped away, and the surface of the bronze is smoothed and finished.
A form of photographic printing used between the 1860s and the 1930s. A sheet of paper is coated with gelatin containing a pigment such as carbon black (hence the name) and potassium bichromate (to make it light sensitive). This can be exposed to daylight under a negative. Exposed areas of the blackened gelatin harden in proportion to the amount of light received; unexposed areas remain soluble and can be washed away, to produce
This process was developed in the early 1840s, although it was not much used until the 1880s-1900s. It involves exposing paper impregnated with iron salts to daylight, in contact with a negative. An image in insoluble Prussian Blue is produced on the paper, which can be fixed by washing in water. It is more familiar as the process used for producing copies of plans and documents known as ‘blueprints’.
Etching is a method of printing from thin metal (usually copper) plates, using the action of acid on the metal to ‘bite’ or cut thin lines into the surface. These lines can be inked and printed onto paper through the great pressure exerted by a type of printing press known as a ‘roller press’.
Gelatin silver prints
Gelatin is a transparent, water-soluble substance made from boiling animal skin and bones, which can be used as a medium to carry light-sensitive materials, such as silver bromide and silver chloride. Papers coated in this way can be exposed briefly under a negative and then developed. This method of producing photographic prints
was used from the 1880s onwards.
This is a method or printing images developed in the early-19th century, which relies on the antipathy of grease and water. The images to be printed are drawn in a greasy medium onto the surface of specially prepared blocks of limestone (lithography literally means ‘stone drawing’).
Parian ware was invented in the 1840s as a way of imitating, relatively cheaply, the white marble from the Greek island of Paros, from which the Parthenon marbles were made. Parian ware statues are made by slip-casting. Liquid porcelain, or slip, is poured into a mould and allowed to harden enough to coat the walls of the mould. The excess is then poured out, creating a thin-walled, hollow form.
This method of using photographic negatives to produce printing plates was used commercially from around 1880. It involved coating a copper plate with bichromated gelatin, and exposing it to light through a photographic negative. The gelatin will harden in proportion to the amount of light it receives, so that the plate can be etched to different depths, and inked and printed with normal printing inks onto untreated paper.
The daguerreotype was the first photographic process to be announced to the public (in 1839). A silver surface on a copper plate is sensitised by fumes from iodine, exposed in a camera, and the image developed by exposure to mercury vapour. The unique positive image appears on the highly polished surface of the silvered plate; this surface is easily damaged by touching, so daguerreotypes were usually held in protective frames or cases. A pair of images of the same subject - taken from slightly different angles and reproduced on the same plate - produced the illusion of a three-dimensional image when looked at through a stereoscopic viewer.
Developed in the late-18th century, wood-engraving is a method of printing from an
image cut in relief on a wooden block. Unlike woodcutting, an earlier method of relief printing, wood-engravers work with much sharper tools on a block cut across, rather than along, the grain, giving a dense, hard surface into which much finer lines, and therefore more finely detailed images, could be cut. The blocks are inked and printed in
a press much like that use for printing type.