Re: Where did early photo chemicals come from?

There is little or no record of concern over chemical purity in the 
wiritngs of early photographic investigators.  Chemical suppliers have 
existed for thousands of years.  Early alchemists, pharmacists, and 
finally chemical manufacturers were providing chemical reagents of all 
kinds long before photographers expanded the market.  Experiments in 
photographic chemistry were begun in 1727, by a German physicist Johann 
Heinrich Schultze.  His experiments into the phenomenon used a dry mixture 
of silver nitrate and chalk dust in a bottle.  When the bottle was exposed 
to light the silver nitrate reduced to silver metal and darkened a thin 
layer just under the glass.  When the bottle was shaken, a fresh layer of 
silver nitrate was brought next to the bottle's interior surface.  When he 
cut paper stencils of letters and words and wrapped them around the 
outside surface of the bottle, the exposure to light darkened the cutout 
area and left the covered parts unaffected.  This left shapes that could 
be clearly seen.  

Silver nitrate is made by dissolving silver metal in nitric acid.  This 
salt was used in 1816 by a Frenchman, Joseph-Nicephore Niepce.  He put 
paper soaked in silver nitrate inside an improvised camera made of a jewel 
box and a lens from a microscope.  His captured image contained reversed 
tones, a negative.  The light areas were recorded as dark and the dark 
areas were recorded as light on the paper.  This problem was solved when 
Niepce used a certain kind of bitumen (coal tar), which reacts to light in 
a peculiar way.  The substance is ordinarly soluble in oil of 
lavender, but after exposure to light it is no longer soluble in this 
chemical.  Niepce coated a pewter plate with bitumen and focused his 
camera upon a subject, exposed the plate and then bathed it in lavender 
oil.  The metal was laid bare only in those areas to which the light had 
not been reflected from the subject.  He then made the metal areas dark by 
passing the palte over fumes of iodine. (Iodine was recovered from ashes 
of seaweed.) 

Niepce met Louis-Jaques-Mande Daguerre and they became partners.  By the 
year 1837, Daguerre developed what he called the daguerreotype process.  
It consists of 1.)  Polishing a silvered copper plate  2.) The plate was 
laid face down on an open box filled with particles of iodine.  
When the surface became straw-colored, it was placed in the camera and  
3.) was exposed, for a time varying from five to forty-five minutes.  In 
semi-darkness the plate  4.) was placed over heated mercury.  The image 
grandually "developed" with the deposit of whitish mercury amalgam in 
those areas where light had fallen.  5.)  To remove the unexposed silver 
salts, the palte was washed in sodium thiosulfate (the called sodium 
hyposulfite) and rinsed in water.  The treated copper plate was the 
photograph.

In 1839, William Henry Fox Talbot published a paper describing his method 
of "photographic drawing."  The process follows:  1.) Good quality writing 
paper was soaked in a weak solution of common table salt (sodium chloride) 
and then wiped dry.  2.) By dim light, a 1-to-6 or 1-to-8 solution of 
silver nitrate was spread on one side of the salted paper.  This paper had 
now become "photogenic" that is, sensitive to light.  3.)  The paper was 
pressed against a flat object, like a piece of lace or a leaf, in a glass 
frame or else it was inserted in a camera obscura.  It was then exposed to 
light until a reddish image appeared.  4.) The unexposed silver salts were 
made relatively insensitive to light by wahsing the paper with a strong 
solution of commons salt.   Talbot obtained a negative picture in this 
way, he obtained a positive picture by pressing the negative against a 
fresh piece of photogenic paper and exposing it to light.  Later, sodium 
thiosulfate was substituted for the desensitizing salt solution.

The early processes described here continued to develop.  Unitl now, the 
photogenic paper was left in the camera until an image could be seen 
before further developing the image.  Gallic acid allowed much shorter 
exposure times by bringing out the "latent" image on the paper and 
enhancing the contrast between exposed and unexposed silver nitrate.
The history of "wet plate" photograhy began in 1851, just in time for the 
Civil War.  The chemicals used in this process included collodion, 
potassium iodide, silver nitrate, pyrogallic acid, and sodium thiosulfate 
or potassium cyanide.  This process required the plates to be exposed and 
developed while the plate was still wet.  This chained the photographer to 
a "tent" or some other darkroom.  It was inconvenient.

"Dry plate" photography was developed in 1871.  This freed the 
photographer to take his pictures and store the plates to be developed 
later.  Dr. Richard Leach Maddox, an English amateur photographer, 
mixed melted gelatin with a bromide salt and added silver nitrate.  The 
emulsion was then spread on a glass plate; when this became dry, it was 
ready to use.  A photographic plate company soon supplied these dry plates 
and would even develop the finished pictures, if desired.

A flexible paper roll was the next logical jump from glass plates.  In 
1888, George Eastman of Rochester, New York, made a photographic paper 
roll that was coated with gelatin-bromide emulsion.  A hundred exposures 
could be made on each roll.  The exposed camera was sent to Eastman where 
it was developed, printed, refilled with new "film" and returned to the 
owner.  

The original paper rolls were hard to process because the gelatin had to 
be transferred to glass before prints could be made.  In 1889, Eastman 
used flexible celluloid film to support the light sensitive gelatin.  This 
eliminated the need to transfer the gelatin.  Prints could be made 
directly from the film.

References:
The Book of Popular Science, The Grolier Society, 1968.
The Little and Ives Complete Book of Popular Science, 1958


Dan Berger adds:

Variable purity in different batches of chemicals from the same supplier was 
apparently enough of a problem in the 19th Century that Robert Louis Stevenson 
used it as an important story point in "The Strange Case of Dr. Jekyll and Mr. 
Hyde." It turns out that the unknown impurities in the chemicals used by Dr. 
Jekyll are the key ingredients in his potion, and he is unable to reproduce his 
transformation using fresh supplies. This finally traps him in Mr. Hyde's body.