(a) The shades or tints between the highest points of light and the deepest shadows of an image; (b) a copper or zinc plate on which is made a reproduction of a photograph, the half-tones being represented by fine dots. Used for illustrating books, newspapers, etc., the reproduction being in one color of ink.


A term used to describe the four elements, bromine, chlorine, fluorine and iodine. These four elements form salts which greatly resemble each other and have other similar properties.

Haloid Salts

(See Salts, Haloid.)

A name given to the salts formed by the combination of a metal with a halogen element. For instance, the union of chlorine with silver forms silver chloride and is, therefore, a haloid salt of silver.

Hand Camera

(See Camera, Hand.)

H. & D

Hurter & Driffield System. A system which has been almost universally adopted in England for testing the sensitiveness of photographic plates. Originated by the two scientists, Hurter & Driffield.


A solution employed for hardening gelatin negatives and papers. Especially valuable in hot weather. Alum, sulphites, formalin and other chemicals have the effect of hardening gelatin.


(See Chalkiness.)


Any arrangement or combination of relative parts or elements that is consistent or is aesthetically pleasing; agreement of particulars according to some standard of consistency or to aesthetic judgment; an accordant, agreeable, or suitable conjunction or assemblage of details; concord; congruity. Harmony is to be distinguished from symmetry: thus, in a symmetrical building two opposite wings are exactly identical, though usually with the architectural members in reverse order, while in a harmonious building the two wings need not be identical in a single detail, if they balance each other so as to form, taken together, a pleasing and consistent whole.

(Century Dictionary.)

Hard Water

Head Rest

An apparatus constructed out of iron. Used for supporting the head in order to prevent movement of the subject during exposure.


A Metric weight or measure containing 100 grammes.


A Metric measure of capacity for liquids.


A Metric measure of length.


(See Lens, Heliar.)


A modification of the collotype process.

High-Lights - VI; VII; X

An art term denoting portions of a picture which have received the greatest amount of light; i. e., that part of the subject on which the light has been concentrated. In the negative these portions are the densest or most opaque.

History of Photography

Hogarth's Line of Beauty

A very common form of composition, based upon the curved form of the letter S.

Plate Holder

A case in which the sensitive plate is carried. After the image has been focused on the ground-glass the plate-holder is inserted in position, the slide which protected the surface of the sensitive plate is withdrawn, and the exposure made, after which the slide is replaced and the holder withdrawn SINGLE plate-holders accomodate only one plate, while in the DOUBLE plate-holder two sensitive plates may be placed.