Galvanography:- technique of electroplating a gelatin relief image created photographically to produce a photomechanical printing plate.
Gamma:- measurement used in sensitometry to describe the angle made between the straight line portion of the characteristic curve of the photograph emulsion and the base of the graph. The gamma is the tangent of the angle so formed.
G curve:- average gradient of a characteristic curve, describing similar characteristics to gamma, but measuring the slope from a line joining the lower and upper limits of the curve actually used in practice.
Gelatin:- natural protein used as a transparent medium to hold light sensitive silver halide crystals in suspension, binding them to the printing paper or film, yet swelling to allow entry of processing solutions.
Gelatin filters:- filters cut from dyed gelatin sheets and held in front of the lens or studio light.
Gelatin sugar process:- daylight printing process using paper with a sugar and dichromate coating, which hardens on exposure to light.
Ghost images:- bright spots of light, often taking the shape of the aperture, which appear in the camera viewfinder or in the final photograph when a lens is pointed at a bright light like the sun. Ghost images have been almost eliminated through the use of multi layer coatings of the lens elements.
Glaze:- glossy surface produced on some (non resin coated) printing papers. It is achieved by placing a wet print to to a heated drum or clean polished surface. Glazed print produce denser medium blacks than their matte counterparts.
Glazer:- machine on which wet fiber base prints are placed face down in contact with a polished surface, such a chromed steel, and held by tension. The surface is then heated to dry the print.
Glossy paper:- printing paper with a smooth shiny surface finish to give maximum detail and tonal range.
Gold chloride:- soluble chemical used in gold toners.
Gold mean:- compositional technique used to determine the "ideal" position of the main subject in the frame. It is based on creating a rectangle from a square. A line drawn from the center of one side of the square to the opposite corner becomes the radius of an arc. The side of the square is then protracted until it meets the arc, and from this point a rectangle is constructed. The side of the square which remains in the rectangle indicates the point at which the subject should be placed.
GOST:- arithmetical system of rating film speed used in Soviet bloc countries.
Graduated filter:- filter with a colored section, which gradually reduces in density toward the center of the filter. The rest of the filter is clear. Also referred to as a Graduated filter.
Gradation:- tonal contrast range of an image.
Grade:- system of terms and numbers used to denote the contrast characteristics of black and white printing papers.
Graduate:- vessel used for measuring liquids.
Grain:- clumps of silver-halide grains in film and paper that constitute the image. These grains are produced both in the exposure process (film grain) and in the development process (paper grain). Unlike film, the grain in printing paper is largely responsible for the image tone.
Graininess:- clumps of silver halide crystals in the emulsion which are visible to the human eye because of spaces between the crystals.
Grains:- exposed and developed silver halides which have formed black metallic silver grains, producing the visible photographic image.
Granularity:- objective term describing the amount that silver halide grains have clumped together within the emulsion.
Gray card:- card with an 18 percent gray tint (reflectance) used to determine exposure by taking a meter reading from subject light reflected by the card.
Ground glass screen:- translucent glass sheet used for viewing and focusing the image on all large format and some reflex cameras.
Guide number:- term sometimes used to describe a flash factor, which provides a guide to correct exposure when using flash.
Gum arabic:- water soluble gum obtained from the Acacia tree and used in coatings of a number of photographic processes.
Gum bichromate:- contact printing process once very popular for the manipulative, impressionistic effects it makes possible. Drawing paper is coated with a mixture of gum, potassium bichromate and a pigment of any chosen color. This is then exposed to light behind a negative. Also known as the photo aquatint process.
Gum platinum process:- combination of gum and platinum printing.
Gyroscopic camera mount:- device employing a gyroscope to help stabilize hand held cameras subject to movement or vibration from outside sources.