This section is from the American Hand Book of the Daguerreotype, by Samuel D. Humphrey. Published S. D. Humphrey, 37 Lispenard Street 1858.
The following is from Humphrey's Journal, vol. 5, and from the pen of Dr. WM. HARRINGTON, one of the most able writers upon the subject of the Daguerreotype in this country:
THE CAUSE OF THE DIFFICULTY THAT SOMETIMES OCCURS TO PREVENT THE PRODUCTION OF A CLEAR IMPRESSION UPON A DAGUERREOTYPE PLATE.
Beyond all doubt this is traceable to dampness. Truly this is not a new thought; but where does this dampness come from? How does it originate, and where is it located? Generally it has been referred to a point entirely remote from its real location.
This dampness exists particularly upon the surface of the plate; is obviously derived immediately from the atmosphere; and is owing to a certain relative temperature of the plate with the hygrometric condition of the atmosphere.
Whenever this relation exists between the plate and atmosphere, a precipitation of moisture takes place upon the surface of the plate, which render all efforts at polishing impracticable. This interference is not confined to the buffing operation alone, but sometimes is discoverable even in the ordinary process of scouring. Every one at all experienced in this art will remember that it is not always an easy matter for him, by scouring, to bring his plate to the desired lustre. All his efforts become unavailing; the more he rubs, the duller the surface of his plate appears; and although he renews his cotton repeatedly, still he is obliged to content himself with an unsatisfactory finish.
This relative condition is not confined to any particular season of the year, nor to any certain thermometric temperature; but may occur in summer as well as in winter; the weather being warm or cold, wet or dry, clear or cloudy, raining or shining. Under any of these circumstances, if the relation of the plate and atmosphere be such as to invite upon the plate a precipitation of humidity from the atmosphere, the prospect of producing a clear impression is quite problematical.
It is reasonable to expect this occurrence from the fact that metal is a good radiator, and radiation reduces the temperature of a metallic body below that of the atmosphere. Consequently, if this relative condition happens, the result will be as I have stated.
Bodies may be colder than the atmosphere and yet derive no moisture from it; while at the same time the driest atmosphere is not devoid of moisture, but will part with it under certain conditions.
Assuming for granted that this relative condition between the plate and atmosphere, disposing the former to receive the humidity of the latter, constitutes the great obstacle the operator has to contend with in producing, a clear proof upon the plate, the remedy naturally suggests itself, and is very simple. It consists in merely heating the plate above the temperature of the atmosphere, previous to polishing, and retaining that temperature during the operation. Various measures might be devised to effect the desired object; one of which consists of a sheet-iron box, heated from the inside by a spirit-lamp, upon the top of which are to be kept the plates ready to undergo the process of being polished; the blocks of the swing or any other vice; or the iron bed belonging to Lewis's vice.
In cold weather, when it is necessary to keep a fire in the preparation room, all of the above may be so arranged in the vicinity of the fire as to receive the requisite degree of heat for the purpose specified.
This part of the subject, however, is left entirely for the ingenuity of the operator. No matter by hat means he accomplishes the object; all that is required is to heat the plate above the temperature of the atmosphere and retain that heat during the process of polishing.
Since the adoption of this method. in connection with my partner, T. J. Dobyns, even in this humid climate of ours, when everything in the room is dripping with moisture, it has been attended with invariable success.