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darkroom - A light-tight area, either completely dark or specially illuminated, for handling light- sensitive materials.

data base - A collection of data organized especially for rapid search and retrieval, usually stored and accessed by a computer.

deacidification - A common term for a chemical treatment that neutralizes acid in a material such as paper and deposits an alkaline buffer to counteract future acid attack. While deacidification increases the chemical stability of paper, it does not restore strength or flexibility to brittle materials. See also pH.

deckle - The natural uneven edge on handmade paper or an edge torn to simulate it. Tearing wet paper against a saw or straightedge is one way to make a deckle edge.

densitometer - A machine used in the science of sensitometry to measure the densities of exposed and processed emulsions. It is the densitometer that enables a photographer to take highlight and shadow readings from processed negatives to determine the density range of the negatives.

densitometer - A device used to measure the optical density of an image or support material by measuring the amount of incident light that is reflected or transmitted.

desiccant - Any agent--particularly a silica gel--that removes gaseous water from the air and that reduces relative humidity. Desiccants can be used in sealed enclosures to protect photographs from humidity. Silica gels can be made to give up their absorbed moisture by heating, and then reused.

developer - A chemical substance in dry, liquid, or gaseous form used to make visible a latent image, after exposure.

dextrin base - Soluble carbohydrate from starch used in adhesives and as sizing in papers and textiles.

diazo - (diazotype, diazotypy white printing): A generic term for films employing light-sensitive diazonium salts for the production of the film image. The image is a dye and thus subject to fading.

die-cut - A cut made with special steel rule dies. The act of making a part or container which is cut and scored to shape by such tools. Also used to denote a board which has been die-cut.

dimensional stability - The quality in a support, such as film, of not changing its size by shrinking or stretching.

doublewall - Reference to corrugated board--using two layers of fluted corrugated board for additional strength and rigidness while minimizing excessive weight.

D-rings - Binder mechanism -using "D"-shaped reclosable rings for 3-ring binders. The straight side of the "D" ensures all pages will be aligned when the binder is closed.

dropspine - Specially designed hinge that allows the spine of a case to lie flat when opened, allowing access to both sides of the case without interference from the hinge.

dry transfer - Typically, the transfer of material caused by contact of one surface against another, usually assisted by pressure. (As in adverse transfer of pigment from one colored surface to another or as in dry transfer lettering.)

dry-mount - A non-aqueous method for mounting artwork. Two types of dry-mount methods exist--heat mount and cold mount. "Heat mount" is a technique used principally to mount photographs by attaching them to a board with dry-mount tissue and heat. The full system uses a dry-mount press. The piece is backed with dry-mount tissue held in place by "tacking" with a small tacking iron and is positioned on the board and placed in the dry-mount press. The press is closed for a timed interval to suit the type of tissue being used. The heat fuses the tissue to both the picture and the backing. "Cold mount" is a mounting technique utilizing a pressure sensitive adhesive to adhere artwork to mounting board. Long-term adhesion and archival characteristics of cold mount adhesives are unknown.

dye couplers - Property of chromogenic (color print) development. The dye coupler is an element in the developer solution which links and chemically reacts with a dye precursor located in the emulsion of the paper to create a color within the print.