DAGUERREOTYPES, CLEANING AND RESTORING Cleaning and restoring a daguerreotype picture is at all times a risky process, and should not be attempted unless the worker is particularly careful and patient. Many methods have been advocated, but they all need care and thought, and rather than run the risk of ruining a picture it is better for the uninitiated to leave the work alone. It must be remembered that daguerreo types are valuable relics, and that comparatively few modern photographers know how they were made. The pictures become indistinct and dull, not by fading, as the modern photographer under stands it, but as a result of the oxidising influence of the atmosphere, which has been unwittingly allowed to act upon them, either because the hermetic sealing was imperfectly executed, or because it has become broken away. In this article is described the method of cleaning and restoring that is considered to be the most reliable, but before any attempt is made to improve the picture the processes by which it was produced should be thoroughly under stood (see "Daguerreotype Process "), the res torer will then know the composition of the photograph. This photograph consists of a most delicate film on the surface of a silvered plate, not varnished or protected in any way, and susceptible of injury from any rubbing or abrasion. Flicking off the dust with a silk handkerchief, or lightly touching the surface with the finger or a camel-hair brush, may ruin the picture. The operator must first try to ascertain whether the picture is in its original state, and whether there has been an earlier attempt to clean or restore it, because should certain chemicals have been left in the film the picture may be ruined when others are applied.
The usual and best method of restoring a faded or discoloured daguerreotype is as follows : Take out the plate from the frame and immerse the discoloured picture in a i per cent, solution of potassium tcyanide in distilled water, care fully rocking the dish until the milky or smoky appearance caused by oxidation disappears. If
the cyanide solution is not strong enough it may be strengthened, but particular care must be taken to use the purest of distilled water, and not to touch the picture with any solid substance, even with cotton-wool. As soon as the discoloration (oxidation) has vanished, the plate must be gently but thoroughly washed in several changes of distilled water, avoiding ordinary water. Finally, it is dried by gentle heat in an atmosphere as free from dust as possible, and in nine cases out of ten the simple treatment will have restored the picture and made it almost, if not quite, as good as new.
If, however, the restored picture lacks brilliance and detail, it may be redeveloped, but as the latter process is particularly risky it should be attempted only in extreme and very bad cases. Redevelopment is done by exposure to the fumes of mercury, and not by the application of any liquid. Procure an air-tight box about 3 ft. high ; at the bottom place a small spirit lamp, and over it a saucer of pure metallic mercury. Carefully fax the plate to be redevel oped to the lid of the box in such a way that the picture is face downwards when the box is closed. Close the box so that the picture may be exposed to the fumes of the mercury, and examine every minute to see how development progresses. When all detail is restored, remove the plate. Care must be taken during this process not to inhale the fumes, as they are poisonous. Lay the redeveloped plate on a piece of clean, clear glass, and bind the edges with silk strips, using Canada balsam as an adhesive ; this binding must be done thoroughly in order to exclude the air. Redevelopment is rarely necessary, and is to be avoided on account of the risk to both plate and operator.