Daguerreian Society

On this day (September 4) in the year 1891, the following article 
appeared as the fifth in a series in "The Photographic Times" (New York; 
pp. 442-3): 
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  HAVING described the art as it was practiced when I first became 
acquainted with it, and having strayed somewhat from my story to make 
some comments upon the durability of its productions as proved by the 
experience of nearly half a century, it may be interesting to refer back 
to the opinion formerly held in regard to the permanency of the 
daguerreotype.  It will be seen that a priori reasoning on that question 
has not been verified by experience.  I will quote from a work on 
chemistry by a professor of this science in the University of Edinburgh:

  "We are of the opinion that daguerreotype pictures are not durable.  We 
know that they soon fade if not covered with gold, and as this stratum of 
gold is infinitesimally thin, it will in time oxidize off and leave the 
picture exposed to the air.  It is not to be supposed that so delicate a 
fabric as one of these pictures should be durable, upon so unstable a 
foundation as two plates of metal between which, so closely juxtaposed 
and so antagonistic in their electrical relations there is such great 
liability to galvanic action."

  It is curious to read this prediction issued from so high a source and 
uttered with so much confidence as to have almost the appearance of a 
scientific deduction.  Still more curious are the reasons given for this 
oracular utterance:  First, the "so delicate a fabric," and second, the 
"so unstable a foundation."  The fabric was silver, mercury, and gold, 
made to unite by heat, and it is doubtful that any other picture produced 
by photography has contained as much substance in its structure as the 
daguerreotype.  The toning bath for example contained fifteen grains of 
the chloride in a quart of water, and the gold was precipitated upon the 
picture by heat in much greater quantity than any silver print could be 
made to take.  I have referred to boiling these pictures in cyanide of 
potassium.  They may also be boiled in sulphuric acid without injury--an 
experiment which I have often made to rid them of some scum which the 
cyanide would not remove.  In short, the time when the gold will be 
oxidized off and the picture left exposed to the air seems to be yet 
somewhat remote.  It is also interesting to note the objection raised by 
this renowned scientist to the unstable character of the foundation upon 
which the poor "daguerreotype picture" must needs rest during the brief 
period which would elapse before it would be deprived of its 
infinitesimal protection of gold by the relentless tooth of the fell 
destroyer, oxygen.  This "unstable foundation" was no less than two 
plates--one of copper and one of silver, "so closely juxtaposed" as to 
form one plate.  Strange to say, it has failed to maintain its early and 
perhaps premature reputation for instability.
  To return to my story:  While learning the first lessons in the 
practical knowledge of the art I was also getting together the requisite 
appliances for putting this acquisition into practice.  What I could not 
obtain on credit I bought with borrowed money or manufactured.  For a 
Daniels battery I procured a copper cup of suitable size and shape at a 
tinsmith's; constructed a mould of wood and paper, and cast a porous cup 
of plaster of Paris which proved to answer the purpose well; cast a 
cylinder of zinc in a sheet iron matrix, and by attaching copper wires to 
the cup and cylinder in the simplest manner possible it wanted only the 
necessary solutions to put it in complete working order.  Then dissolving 
a sufficient quantity of silver coin in nitric acid I precipitated the 
chloride with common salt, which left the nitrate of copper (the alloy of 
the coin) in the solution.  After washing the chloride with several 
changes of water until no blue color was visible nor became visible on 
adding a drop of ammonia to the water, the chloride was mixed with an 
excess of carbonate of sodium in a crucible, and on heating it 
sufficiently a button of pure silver was obtained, which being hammered 
out into a plate on a clean anvil it was attached to the positive pole of 
the battery.
  A supply of hydrofluoric acid was also required.  This was produced as 
follows :
  A quantity of pulverized fluor spar (fluoride of calcium) was placed in 
a leaden retort; to this was added about three parts common sulphuric 
acid.  The retort was made in two parts, the upper part fitting over the 
lower, and after being charged, the joint was luted with clay.  The neck 
of the retort was fitted to that of the receiver by a ground joint and 
the receiver was surrounded with ice and salt or ice-cold water.  Then on 
applying a gentle heat to the retort, which was placed in a sand bath 
under a flue, the acid was generated and passed over into the receiver.  
The acid was, of course, kept in a bottle of lead.
  I also made up a small stock of chloride of gold.  A piece of gold coin 
was dissolved in three parts of hydrochloric acid to one part of nitric 
acid (each of these parts being equal in weight to the gold).  The 
solution was then decanted from the flask, leaving the precipitated 
chloride of silver (from the alloy) which was washed with several changes 
of water and this water added to the other solution.  The copper of the 
alloy being in solution with the gold was separated from it by adding an 
excess of a saturated solution of copperas filtered and made clear by a 
few drops of sulphuric acid.  This precipitates the gold in the form of a 
dark brown powder, which being also washed to free it from the copper and 
iron, is redissolved in the nitrohydrochloric acid as before.  As the 
American gold coin is one-tenth alloy it is easy to determine the amount 
of pure gold and of pure terchloride that should be obtained from it.  
For example a five dollar piece weighs 129 grains.  Deducting one-tenth 
we have 116 grains of pure gold, and this should give 178 grains of pure 
chloride.  If now after the gold is redissolved a quantity of dried table 
salt equal in weight to that of the pure chloride due from the gold be 
dissolved and added to it the mixture will be a solution of chloride of 
gold and sodium, and when evaporated nearly to dryness the double salt 
will be in a convenient form for handling and use, and in all respects 
equal for use to the pure and much more deliquescent single chloride.
  At the present day, if wanted for toning photographs, it is better to 
leave the copper and not separate it from the gold.  Find how much pure 
chloride of gold is due from the coin; and add the salt to the first 
solution described above as when freed from the chloride of silver, 
making no account of the copper; then evaporate down as before directed.  
The rule for finding the chloride, the weight of pure gold being given, 
is as follows:
  As 200, the combining weight of gold, is to 306.5, the combining weight 
of the terchloride, so is the weight of the gold given to that of its 
chloride.  As in the above, 200: 306.5:: 116: 177.77.
  In reality the quantity of chloride obtained is much greater.  The 
formula gives only the weight of the anhydrous salt, and the difference 
between this and that obtained by the process described affords a 
handsome profit.  I have found that 30 grains of the double salt are 
fully equivalent in toning power to 15 grains of the pure chloride from 
the most reliable houses.

                                                W. H Sherman.
                       (To be continued.)

(Previous installments appeared on Jan 20, March 13, April 17, and May 15
and were posted to DagNews in 1997 on the date of their original 
publication. The sixth installment will appear on September 18.)
Posted for your enjoyment.     Gary W. Ewer     

Return to: DagNews 1997

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