On this day (May 15) in the year 1891, the following article appeared as 
the fourth in a series in "The Photographic Times" (New York; pp. 183-
5): 
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           THE RISE AND FALL OF THE DAGUERREOTYPE.

              AS SEEN BY A COUNTRY "OPERATOR."

                            IV.

  The mercury bath consisted of an iron vessel in form of a hopper, a 
little larger at the top than the largest plate, and a little deeper 
than the length.  A rod from the side of this to the side of a circular 
base supported it directly over the latter, on which stood a small 
spirit lamp with a flame-regulating tube.  The bottom of the vessel was 
formed into a small cup in which was placed about an ounce of pure 
mercury, which was frequently filtered through a cone of clean paper 
perforated at the apex with a needle, through which fine aperture the 
liquid metal ran, leaving dust and dross behind.  The cup containing 
this was kept about blood-warm by a tiny flame during working hours, but 
when a plate had been exposed in the camera the plate holder was taken 
to the mercury bath and placed, face down, over the top, the slide drawn 
and the flame of the lamp increased a little.  This was usually done in 
what was then called the dark room, but the light needed only to be 
weak; the plate could be safely developed in a place distant from a 
window and but little screened from the light.  A thermometer was 
furnished with the mercury bath, but was almost always broken in a short 
time, and of course but little used, the hand being a handier and quite 
as reliable a test.  The temperature was raised, not too rapidly, to 
about 150 deg. Fahr.  The operator soon learned to judge by the sense of 
touch when the vessel was hot enough, and could then light a match, and 
raising the plate a little, see whether it was fully developed or not.  
The operation was very simple and admitted of little variation--not even 
as much as the development of a wet plate.  It did not appear to consist 
in the reduction of the silver from the haloid impressed with the light 
as in the modern dry plate, and was certainly unlike the manner in which 
the image is formed on the wet plate, which chiefly consists of silver 
derived from the free nitrate and deposited on the foundation traced by 
the actinic rays.  The silver plate, covered with a coating of iodo-
bromide of silver and not exposed to the light, was impervious to the 
vapor of the mercury, but after it had been impressed with the image of 
the camera, the molecules of the sensitive coating were so changed as to 
allow the evaporated mercurial atoms to pass between them to the plate 
beneath in obedience to the affinity of the two metals for each other.  
When we think of it, all this is wonderful.  We are led to ask, How does 
the image in the camera affect this coating so that without any visible 
change it does open its doors to the rising particles which otherwise 
would knock in vain for admittance?  Where the light was too strong, as 
from a broad white shirt front, for instance the image was often lost by 
solarization; that is, so much mercury united with the silver in that 
space as to produce a flat dead blank without detail.  This defect was 
sometimes remedied by using a false front of light nankeen.
  The plate, after being taken from over the mercury, could be shown to 
the sitter, much as a chemical proof can now be shown, but with much 
greater precaution, lest it should be marred in the slightest degree.  
If not satisfactory it was set aside to be rescoured and repolished, and 
a new plate taken for another sitting.  It was customary to have on hand 
a supply of plates ready for the last short buffing which it was 
necessary to give them the last thing before coating, not only to remove 
any dust but also any effect the atmosphere may have produced upon them 
while waiting to be used.  If portraits were to be taken the last 
buffing was across and not lengthwise of the face.
  When the likeness was found to be worthy of approval, it was fixed by 
immersing it in a solution of hypo, and it was quite as readily seen 
when the fixing was completed as it is when that of a negative is done.  
It was then washed with clean water, when it was ready for gilding.
  The gilding solution was made as follows: Fifteen grains of chloride 
of gold were dissolved in 16 fluid ounces of pure water.  In an equal 
quantity of water 55 grains of hyposulphite of sodium were dissolved, 
and to this was added, a little at a time, with frequent stirring, the 
gold solution.  The whole became colorless in a short time.  The edges 
of the plate having been bent up before fixing, it was held at one 
corner by a pair of pliers in a horizontal position and covered (while 
wet from the washing) with the gilding solution which was then uniformly 
heated by passing underneath it the flame of a spirit lamp.  Small 
bubbles caused by the heat soon covered the surface of the plate and the 
tone of the picture visibly improved, the high lights became more 
brilliant, the shadows deeper.  As soon as the bubbles disappeared the 
heat was withdrawn.  After waiting a moment the solution was thrown off 
and the plate thoroughly washed and then dried over the lamp.
  Then, as now, the most beautiful result was not quite satisfactory.  
But there was one great advantage possessed by the daguerreotype: the 
wrinkles and characteristic lines could not be obliterated by the 
retoucher's pencil.  The mouth could not be shortened, the hollows of 
the checks filled up; the nose reduced, eyebrows retrenched, the old 
face made to look young, nor in fact any of the abominable defacements 
and falsifyings practiced, which are now so common, and which I cannot 
help thinking have much to do with cheapening and demoralizing the art 
of photography.
  A perfect daguerreotype needed no artificial aid to its beauty, but it 
was customary, and usually required, to give a little color to the lips 
and cheeks as well as to touch the rings and other jewelry with gold, 
which, though not strictly in good taste, was quite harmless, as it 
could be easily removed at any time if so desired.
  Probably no picture ever made was more lasting than this, when 
properly finished.  I have many which have been made more than forty 
years that are as bright and perfect as when first made.  But they 
cannot be long kept exposed to the action of the air, this being charged 
with impurities by which the surface of the plates are susceptible of 
discoloration.  It was therefore necessary to protect them; and for this 
purpose a supply of white plate glass cut to the exact sizes of the 
silver plates used was kept on hand, with corresponding mats, preservers 
and cases.
  To put up the finished picture the mat and glass were placed over it 
and the three bound together with strong adhesive paper which secured 
the edges and lapped over on to the back.  This was followed with the 
metallic preserver, which framed the glass in front with a neat border 
and was wide enough to bend down also on the back and so form a 
protection to the sealing paper.  Finally, all was pressed into the 
case, when the work was ready for delivery.
  Experience has proved several interesting facts in relation to 
daguerreotypes.  One of these is, that neither light nor age appears to 
have any injurious effect upon them.  I have some very old ones that 
were hung outdoors on the south side of a building for years, and which 
are still in a perfect state of preservation, apparently unchanged.  It 
is a curious fact that most of these in my possession which were put up 
in contact with brass mats have become much discolored under the mats, 
the discoloration spreading inwards upon the picture to a greater or 
less distance.  Some with paper mats have been similarly affected, while 
others have escaped.  The inference from all my observations has been 
that if protected from dampness and the sulphurous gases which pervade 
the atmosphere, a properly finished picture of this kind is 
imperishable.  Those that have lasted forty or fifty years unchanged 
are, or seem to be, in themselves reasonable proofs that they may last a 
thousand.  Even those which have become much tarnished may be quickly 
restored to their original brilliancy by immersing them in a hot 
solution of cyanide of potassium, a treatment heroic enough to speedily 
wipe out almost any other species of the photographer's art.  If any 
should wish to restore an old daguerreotype by this process, he should 
clean off all the paper from the back, and be careful to use cyanide 
that is not partly decomposed, as shown by an ammoniacal smell (good 
commercial cyanide which is dry and solid is suitable); above all it 
must not have been used for fixing, lest the picture by spoiled by scum 
of silver deposited from the solution.  Dissolve about half an ounce of 
cyanide in a pint of water, and heat in a porcelain evaporating dish.  
Immerse the plate, face up, move the dish, continuing the heat until the 
color disappears, then remove the plate and wash it thoroughly under the 
tap.  It can be dried by leaning it cornerwise and nearly upright in the 
top of a graduate, or in the old way by holding it at the corner with a 
pair of pliers, and heating it from the top downwards.

                                                W. H Sherman.
                       (To be continued.)

(Previous installments appeared on Jan 20, March 13, and April 17 and 
were posted to DagNews in 1997 on the date of their original 
publication. The fifth installment will appear on September 4.)
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Posted for your enjoyment.     Gary W. Ewer     
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05-15-97