DEVELOPMENT OF THE LATENT IMAGE.

On the removal of the plate from the camera no image is visible, it has to be developed. This operation is nothing more than giving an increased density and depth to an exceedingly faint and delicate impression which the light refracted through the lens of the camera has defined upon the iodide of silver in the film; it is, in fact, a continuation of the action of light, which action is the commencement of the reduction of the iodide of silver contained in the collodion to the metallic state, carried on, when thus commenced in the camera, by the reducing agent employed.

We have now to bring out this image. The developing liquids made from formula 1,2,3, as given in the preceding division of the subject, will effect this object.

Take a small quantity of the solution to be used, in a porcelain cup or glass measure, and pour it over the surface of the plate; this should be done with a quick and steady motion of the hand; beginning at the nearest left-hand comer of the glass, giving it, at the same time, a tilting motion, to assist in covering the glass evenly. Precise and certain directions cannot be given when to stop the action of the developing liquid, although there are indications which the operator will detect after he has acquired some little experience from practice, sufficient to tell when it has done its work.

During the progress of the development on the plate it should be examined, to ascertain whether the more delicate shades of the view are coming out. Whilst the attention is being directed to this point, the parts of the picture which have already appeared may be left to themselves; for the chief difficulty will be to bring out the more delicate markings of the shadows, as these are the parts which will be the latest to make their appearance on the plate. The action of the developing liquid should, therefore, be continued until these faint impressions are visible; if, however, the liquid has become entirely decomposed before this is accomplished, it may be poured off, and a fresh supply, with two or three drops of nitrate of silver solution added to it, poured on ; this fresh dose will probably bring out the faint parts as desired.

If, after fixing the image, it is found that the faint and delicate markings of the shadows have not been developed, it must be concluded that the exposure in the camera has been too short; consequently, the next plate must be kept longer in the camera. Sometimes a difficulty is experienced in getting the plate covered sufficiently quick, although the developing liquid has got a proper proportion of acetic acid mixed with it; this often is caused by the plate having been removed to the camera before it is quite saturated in the exciting bath; or from the plate having become too dry, from long exposure in the camera.

A slight immersion in the silver bath after exposure in the camera, just before pouring on the developing liquid, will remedy this fault. Another reason why the developing liquid will not flow evenly over the plate is, that the exciting bath has acquired, from constant use, a large quantity of alcohol, which is thrown out from the film during its saturation in the bath; this defect will be quickly produced, when using a prepared collodion having a large proportion of alcohol in it.

The addition of a small quantity of alcohol to the developing liquid will often be found a remedy; but if this is not sufficient, the solution of nitrate of silver should be boiled either in a German beaker or porcelain dish, to drive off the alcohol. The liquid will, of course, be reduced in bulk by this operation, but if it is measured previous to commencing, water can afterwards be added to make up the original quantity.

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