The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Dragon's Blood
Drying Box
Dragon's Blood. A red resinous substance which exudes from several plants, and is used as a resist in photographic etching processes.
Draining Racks. See Racks.
Drop as Measure. See Weighing and Measuring.
DrOp Shutter. See Shutter.
Dry Collodion methods. See Collodion Processes.
Dry Plates. Glass of particular size coated with a film of gelatine in which a sensitive salt of silver is emulsified. These are to be bought, commercially, so perfect in preparation that but few amateurs will be tempted to coat their own, but the formulae given under Emulsion will be found all that can be desired, and the manufacture of emulsion is an education which all operators if time and circumstances permit, should undertake. It is advis-able for all workers to examine the plates that they intend to use, especially when starting on a tour, to determine one or two points. Plates should be examined as to whether they are cut to size correctly or not, whether they are evenly coated, this being done by holding the plate or one or two plates in turn, before the dark-room light, and seeing whether one part lets through more light than another. Freedom from fog is another essential, and the best way to test this is to take out a plate from a freshly opened packet in a very dim red light, and place in a dish, and develop with freshly mixed ferrous oxalate or pyro-soda developers of normal strength for the normal time, and then see whether it be free from fog or not. With regard to the sensitive-ness of the emulsion this is usually determined and marked by the maker. (Very full particulars as to the making of the modern dry plate are to be found under the heading Emulsion.)
Drying Box. A light-tight box used for drying plates, etc., coated with a sensitive film. There are many different kinds, but the following will answer well: - Make a box of half-inch deal, 2 ft. long by I ft. wide and I ft. deep, with a door opening at one side, with a deep fillet to prevent the ingress of light; at the bottom pierce about twelve holes, and have a second bottom made, but with openings at the side. In the centre of the top have a two-inch gas or zinc pipe fixed with an elbow joint, and