Transparency

(a) Spoken of a substance through which rays of light can pass, and through which objects are visible. (b) A positive picture on glass. A lantern-slide is a transparency.

Trichromatic Plates

(See Plates, Panchromatic.)

Trifocal Lens

(See Lens, Triple Convertible.)

Trihydroxybenzine

(See Acid Pyrogallic.)

Trimmer

An instrument used for cutting or trimming prints.

Triplet Lens

(See Lens, Triple Convertible.)

Tripod

A standard or support having three legs. The legs are usually made in sections, so that the tripod can be folded into small space for carrying. A tripod is used especially for outdoor work.

Tilting Tripod Head

A piece of apparatus consisting of two boards hinged together. One of the boards is fastened to the tripod head, while the other is attached to the camera. By means of side braces it is possible to tilt the camera at any angle and hold it in such position for making exposure.

Tripoli

A siliceous substance used in polishing metals, glass, etc. It consists of decomposed, impure limestone, practically the same as rotten-stone.

Troy Weight

(See Weight, Troy.)

Tungstate of Soda

(See Sodium Tungstate.)

Turpentine

Yellowish, greenish or bluish-green translucent viscid liquid; aromatic odor. Hot, pungent, somewhat bitter taste. Becomes hard and brittle on long exposure to air. Soluble in pure alcohol. Distilled turpentine is termed spirits of turpentine. Used as a solvent for varnishes.

Twin Lenses

(See Stereoscopic Views.)

Ultra-Red Rays

(See Rays, Ultra-Red.)

Ultra-Violet Rays

(See Rays, Ultra-Violet.)

Unar Lens

(See Lens, Unar.)

Under-Exposure

(See Exposure, Under.)

Uniform System

A method of numbering diaphragm openings. F. 4 is taken as the standard, and termed No. 1. The numbers are termed the U. S. numbers.

Universal Focus

(See Lens, Fixed-Focus.)

Universal Lens

(See Lens, Rectilinear.)

Unsymmetrical Lens

(See Lens, Unsymmetrical.)

Uranium

A metal. Black granular mass. When united with nitrate is used for toning and as an intensifier.

Uranium Nitrate

UO2(NO3)2 + 6H2O

Lemon-yellow, fluorescent, rhombic prisms. Soluble in water, alcohol and ether. Used in the uranium printing process in toning; also as an intensifier.

Uranium Toning

A method of obtaining warm tones on bromide and developing papers. The tones, however, are not permanent.

U.S

(See Uniform System.)

Vanadium Chloride

2VO24HC1 + 3H2O.

Dark-green, syrupy mass. Soluble in water and alcohol. Used for obtaining green tones on bromide prints.

Varnish

There are various kinds of varnishes used in photography, and the following formula will be found of value for the various purposes for which they are designated:

'Aluminum, Black Varnish for. First clean the aluminum with fine emery powder. Wash well and dip quickly in the following solution:

The metal should be quickly withdrawn from the mixture and allowed to drain. If not dark enough, repeat the operation. When the color is deep enough dry off the aluminum with fine saw-dust; then lacquer.

Dissolve the shellac in half of the alcohol and moisten the other ingredients with the balance. As soon as the shellac is dissolved, mix and shake all well until thoroughly mixed.

'Another good black varnish is

Black for Cameras. This black is for either the inside or outside, as well as for wood or leather.

Mix the dyes with the alcohol, then add the aniline and heat in a water bath until completely dissolved. Apply with a brush or flannel. Dry near a fire, or by exposure to the sun.

Black for Wood or Leather. Mix lamp-black and French polish in a mortar. The more black employed the deader or more mat will be the surface, while the less of the lamp-black the brighter or more glossy will be the black; but if too much lamp-black is used it will easily rub off.

Brass, to Blacken. (See Brass.)