[pure-silver] Re: Rodinal
- From: `Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Mon, 20 Apr 2015 18:33:27 -0700
On 4/20/2015 5:47 PM, Janet Gable Cull wrote:
Thank you, and thanks to all for the interesting and helpful info!
Janet
A caveat: In Ed Buffaloe's article he says that Rodinal uses
sodium hydroxide as the accelerator. Probably it contains potassium
hydroxide. This is likely because the potassium salt can be dissolved
to a higher concentration than the sodium salt and because Agfa used
potassium salts a lot since they produced potassium in large quantities
as a by-product of their other chemical manufacture. Also, silver
solvent action has nothing to do with fine grain. It takes a lot of
silver solvent action to have any effect on the image and some is
necessary for the developing agents to gain access to the sensitivity
cores (not the right term but I can't think of the right one) in the
silver halide crystals. There is an optimum amount of solvent action
which results in the highest speed. One reason D-76 delivers good speed
is due to the solvent action of the relatively large amount of sulfite
in it. The salt action of the sulfite and borax combine to reduce
swelling and improve the grain. Rodinal does not have a lot of sulfite
in it but could not function without some and would oxidize very quickly
without it.
P-aminophenol is closely related to Metol, AKA Elon, which is
p-(methylamino) phenol sulfate AKA a number of other names. Metol is a
trade name used by Hauff and probably Agfa, Elon was the Kodak trade
name for either the same thing or something very close.
Prior to 1851 non-organic or inoganic developers such as ferrous
oxalate were used. In 1881 Pyrogallic acid, an organic reducing agent
of the polyphenol class, was discovered by von Regnault and Scott
Archer. It very rapidly supplanted all inorganic developers and remained
the primary developing agent until the aminophenols began to be
discovered in 1881 but Andreesen and others. After this there was a
rapid proliferation of organic developing agents. Of hundreds of agents
only a few have ever been widely used. The most familar are Pyro,
hydroquinone, Metol, p-phenylenediamine , diaminophenol (Amidol) and
more recently ascorbic acid and Ilford's phenidone
(l-Phenyl-3-Pyrazolidone) Actually, phenidone was discovered in 1890 but
an economical method of manufacture was not devised until the late 1940s.
All of this illustrates the remark by C.E.K. Mees of Kodak
Laboratories that the large number of developers only showed how many
ways there were of doing exactly the same thing.
A list of developing agents as of 1939 can be found in _Handbook
of Photography_ Keith Henny and Beverly Dudley, McGraw-Hill Book
Company. This book also has a long discussion of developers and their
invention up to the time of its printing. I believe but have not
checked, that it is available on-line. Note that much has changed in
the understanding of both photographic chemistry and organic chemistry
in general but there is still much of value there.
Note that p-phenylenediamine was used primarily as an
extra-fine-grain developer before about 1945. It has the property of
delivering exceptionally fine grain but as the expense of great loss of
speed. However, it also has the property of reacting with certain other
chemicals to produce dyes in proportion to development so it became the
parent of a great variety of developers used for color films. The color
developers are modified to improve the speed and to reduce the toxicity
of the parent.
As I write I am finding all sorts of stuff popping out of my
memory that I have not thought of in years. Forgive me if some of this
is repetitive.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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