The portrait, or portion of it, developed upon the pure silver, being much lighter or whiter than that developed upon the alloy;it therefore appeared that the purer the silver, the more sensitive the plate became. Accordingly, we directed Messrs.
Scovills, of Connecticut, to prepare a roll of silver-plated metal, with pure silver; it fortunately proved to be a good article, but, unfortunately, a pound of this metal (early in 1840)cost the round sum of $9. Like descriptions of metal, the same gentlemen would be glad to furnish, at this time, for $4. Soon after this, some samples of English plated metal, of a very superior quality, came to our possession, and relieved us from the toil of making and plating one plate at a time, an expedient we were compelled to resort to, to command material to meet the pressing demands for portraits.
Having it now in our power to obtain good plated metal, a more rapid mode of polishing than that recommended by Daguerre was attempted as follows:
This metal was cut to the desired size, and having a pair of "hand rolls"at hand, each plate, with its silvered side placed next to the highly polished surface of a steel die, was passed and repassed through the rolls many times, by which process a very smooth, perfect surface was obtained.
The plates were then annealed, and a number of plates thus prepared were fastened to the bottom of a box a few inches deep a foot wide, and eighteen inches long; this box was placed upon a table and attached to a rod connected to the face plate of a lathe, a few inches from its centre, so as to give the box a reciprocating motion. A quantity of emery was now strewn over the plates, and the lathe set in motion.
The action produced wag a friction or rubbing of the emery over the surface of the plates.
When continued for some time, a greyish polish was the result.
Linseed, when used in the same manner, gave us better hope of success, and the next step resorted to was to build a wheel and suspend it after the manner of a grindstone.
The plates being secured to the inner side of the wheel or case, and as this case revolved, the seeds would constantly keep to the lower level, and their sliding over the surface of the plates would polish or burnish their surfaces. This, with the former, was soon abandoned; rounded shots of silver placed in the same wheel were found not to perform the polishing so well as linseed.
Buff-wheels of leather with rotten-stone and oil, proved to be far superior to all other contrivances; and, subsequently, at the suggestion of Professor Draper, velvet was used in lieu of buff leather, and soon superseded all other substances, both for lathe and hand-buffs, and I would add, for the benefit of new beginners that those who are familiar with its use, prefer cotton velvet.
The only requisite necessary is, that the buffs made of cotton velvet should be kept dry and warm.
The greater number of operators, with whose practice I am familiar, use, for polishing plates, prepared tripoli, imported from France, or Browne's rotten-stone. The former of these articles is very objectionable, inasmuch as there is no positive certainty of being enabled to procure or make the article of uniform grit--the nature of the substance rendering, it impossible to reduce it to varying degrees of evenness, by the well known process of washing, for that purpose, and the burning of rotten-stone changes its chemical nature somewhat, at the same time rendering, this invaluable article harsh and gritty.
And especially, no reliance can be placed upon burned rotten stone if purchased from those who do not give very great attention and care to its preparation; and the same remarks apply to rouge.
The best article for polishing Daguerreotype plates is rotten-stone, such as can be procured in any town, prepared after the following manner: Procure, say half a dozen wide-mouthed bottles, of suitable dimensions, numbering each from one to six.
Put into No. 1 about half a pound of rotten-stone. and nearly fill the bottle with water. Then, with a proper stick or spatule, mix well the rotten-stone and water; after which, let No. 1 rest for, say one minute, then carefully pour off into bottle No. 2(or, what would be better, draw off by a syphon) as much of the floating particles of rotten-stone as is suspended in the water.
Again fill bottle No. 1 with water, agitate it as before, and decant it to bottle No. 2, care being taken to draw off only the suspended particles of rotten-stone.
When a sufficient quantity of washings from bottle No. 1 is collected into bottle No. 2, a similar process must be gone through. as above stated, for No. 1; the difference being in the care required, and in the time allowed between the stirring or mixing the rotten-stone and water.
The floating particles of rotten-stone, after four minutes' subsiding, will be found fine enough for the finest Daguerreotype polishing required.
A quantity of such washings may be collected in a large bottle, and allowed to stand a few hours, when all the rotten-stone will have settled. The water may be poured off and the rotten-stone put into an evaporating dish, and while being dried, must be constantly stirred to obtain an impalpable powder.
Further washings may in like manner be resorted to for finer qualities of rotten-stone. In my practice, I have used the articles at two and four minutes' settling, and occasionally have prepared it after standing for eight minutes.
So fine a quality as this, however, is seldom required.
In using, rotten-stone, I mix with it, for polishing, fine olive oil, until I obtain a thin paste--and the best of all methods for polishing (well planished) Daguerreotype plates, is one like that used for glass by lens polishers; that is, by using a disc or buff-wheel, and having, a suitable holder by which to secure the plate, and then by pressing the plate against the revolving buff, well saturated with the mixed oil and rotten-stone, a very good surface is obtained.
