Under Exposure

1; II.

Sensitive materials, such as plates or papers are underexposed, if they do not receive a sufficient amount of light action. (See Exposure.)

Extension

The distance to which the bellows of the camera may be drawn out or extended.

Double Extension

A camera so arranged that a bed may be lowered or attached to both front and rear of the body of the camera, or a camera whose bed can be extended almost double its normal length. This gives approximately double the usual length of bellows and allows of extra long focus lenses being used.

Ruby Fabric

A translucent cloth given a red color by dyeing. Used for dark-room windows.

Factorial Development

A process of developing the photographic plate by noting the time of first appearance of the image and dividing this amount into the total time required to complete the development. This gives the developing factor for the developing formula. This factor may be employed at all times when using this particular formula, at the same temperature.

Fading

A defect to which negatives and prints are subject. Usually caused by insufficient fixing as well as insufficient washing after fixing.

Fahrenheit Thermometer

(See Thermometer, Fahrenheit.)

Falling Front

(See Front, Rising and Falling.)

False Perspective

(See Perspective, False.)

Ferric Ammonium Citrate

Fe2(NH4)2(CeH5O7)3 or

Fe(NH4)3(C6H5O7)2.

Ammonium-Citrate of Iron. Brownish-red glistening scales, or green scales - the latter is preferable for photographic purposes. Soluble in water; insoluble in alcohol. Used in the preparation of blue print paper.

Ferric Chloride

FeCl3 + 6H2O. Iron Perchloride. Deliquescent, orange-yellow crystals. Soluble in water and alcohol. Used as a negative reducer.

Ferric Nitrate

Fe(NO3)3 + 18H2O. Iron Nitrate. Grayish-white crystals. Soluble in water. Used as a sensitizer in the various iron processes.

Ferric Oxalate

Fe2(C2O4)3. Iron Oxalate, Ferric.

Greenish-yellow scales or powder. Soluble in water. Ferro-Prussiate Process.

(See Blue-Print Process.)

Ferrotype

A process in which collodion positives are made upon ferrotype plates instead of glass.

Ferrotype Plates

A thin sheet of iron coated with black enamel. Used instead of glass to enamel gelatin prints. Also used for making tintypes.

Ferrous Oxalate

FeC2O4 + 2H2O. Iron Oxalate, Ferrous. Pale-yellow, odorless, crystal. Soluble in cold hydrochloric and hot diluted sulphuric acids; practically insoluble in water. Used in conjunction with potassium chloro-platinite for coating platinum paper.

Ferrous Sulphate

FeSO4 + 7H2O - II; V.

Large, bluish-green efflorescent crystals; odorless; saline astringent taste. Soluble in water; insoluble in alcohol. Used largely as a developer for wet plates, ferrotypes and in the ferrous oxalate developer for plates and bromide paper.