A Manual of Photographic Chemistry, Including the Practice of the Collodion Process

by T. Frederick Hardwich

[CHAPTER VII.]

ON POSITIVE AND NEGATIVE COLLODION PHOTOGRAPHS.

The terms "Positive" and "Negative" occur so frequently in all works upon the subject of Photography, that it will be impossible for the student to make progress without thoroughly understanding their meaning.

A Positive may be defined to be a Photograph which gives a natural representation of an object, as it appears to the eye.

A Negative Photograph, on the other hand, has the lights and shadows reversed, so that the appearance of the object is changed or negatived.

In Photographs taken upon Chloride of Silver, either in the Camera or by superposition, the effect must necessarily be Negative; the Chloride being darkened by luminous rays, the lights are represented by shadows.

The following simple diagrams will make this obvious.

Fig. 1.Fig. 2.Fig. 3.

Fig. 1 is an opaque image drawn upon a transparent ground; fig. 2 represents the effect produced by placing it in contact with a layer of sensitive Chloride and exposing to light; and fig. 3 is the result of copying this negative again on Chloride of Silver.