Gelatin: a substance produced from animal skins and bones, it is the basis for modern photographic emulsions.  This holds the light-sensitive silver halide crystals in suspension.

Glossy:  describes a printing paper with a great deal of surface sheen.  Opposite:  matte.

Graded-contrast paper:  printing paper that produces a single level of contrast.  To produce less or more contrast, a change has to be made to another grade of paper.  See also: variable-contrast paper.

Graininess: in an enlarged image, a speckled or mottled effect caused by oversized clumps of silver in the negative

Gray card a card that reflect a known percentage of the light falling on it.  Often has a gray side reflecting 18 percent and a white side reflecting 90 percent of the light.  Used to take accurate reading (meters base their exposures on a gray tone of 18 percent reflectance) or to provide a known gray tone in color work

Ground glass:  1) a piece of glass roughened on one side so that an image focused on it can be seen on the other side.  2) the viewing screen in a reflex or view camera

Guide number: a number used to calculate the f-setting (aperture) that correctly exposes a film of a given sensitivity (film speed) when the film is used with a specific flash unit at various distances from flash to subject.  To find the f-setting, divide the guide number by the distance

Gum bichromate process:  an early photographic process revived by contemporary photographers.  The emulsion is a sensitized gum arabic solution containing color pigments.  The surface can be altered by hand during the printing process.  Also called gum dichromate.