[rollei_list] Re: Developer 130
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Thu, 30 Oct 2008 09:15:32 -0700
----- Original Message -----
From: "X.TRUONG" <truongthx@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, October 30, 2008 2:40 AM
Subject: [rollei_list] Re: Developer 130
Thank you very much Mr. Knoppow.
My mail server had some problems
I saw some thing about the chemistry, metol make the print
sofer,
hydroquinone make more contrast, borax make film harder,
postassium bromide
prevent the highlight of first print??? Or sodium sunfit
make the film or
print clearly... Please give me something about these...
Best regards,
Xuan Truong
Well, the chemistry of developers is rather more
complicated than this. I am not sure what books I can direct
you to since the better ones are pretty old now. The
understanding of photographic chemistry has changed a lot in
the last twenty years so, to a real chemist, the older books
are pretty outdated. Still, they give a good idea of the
function of the various parts of the developer at a more
elementary level.
The relative contrast given by Metol or hydroquinone is
partly due to the pH of the solutions they need to work.
Generally, the more alkaline developers tend toward higher
contrast. Metol will work in a neutral, or even slightly
acid solution while hydroquinone needs a quite alkaline one.
But, there is more: these two developers tend to react with
each other when used in combination in a way that does not
necessarily affect contrast but does affect the capacity of
the developer and other characteristics because they tend to
regenerate each other. The same is true of some other
combinations such as Phenidone and hydroquinone and either
Metol or Phenidone with ascorbic acid. A combination
developer can be made to have a wide range of contrast, for
instance D-76, a low contrast film developer and Dektol, a
relatively high contrast paper developer, are both Metol and
hydroquinone types.
Borax is a relatively low pH alkali used mainly in film
developers. AFAIK it was first used in Kodak D-76. D-76 is a
relatively low contrast developer with fairly fine grain and
good film speed. While it was originally designed for fine
grain motion picture use it has become as close to a
universal film developer as there is. More contrasty or more
active developers usually rely on an alkali with high pH
than Borax, for instance, the alkali in Dektol is sodium
carbonate. In really high contrast developers, like Kodak
D-8 one finds sodium hydroxide. This developer is intended
for copy negatives of line work (drawings) with little, if
any, gray scale. Its also a Metol and hydroquinone type.
Potassium bromide is a fog suppressor also called a
restrainer. Restrainers tend to reduce the number of
_unexposed_ silver halide crystals that develop along with
the image. If much bromide is used some of the low exposure
image crystals will also be suppressed. Film developers tend
to have the minimum amount of bromide necessary to eliminate
fog and some developers, D-76 for instance, usually do not
contain bromide. This is because bromide tends to reduce the
usable film speed. Print developers have more because fog in
a print veils the highlights and is very undesirable.
Bromide comes out of film when its developed and accumulates
in the developer. It tends to reduce fogging but also
reduces the film speed especialy in the shadows. Some
developers are more affected by bromide than others. For
instance, Metol is relatively unaffected while hydroquinone
is strongly affected so one finds lots of bromide in very
high contrast developers which use bromide. There are more
modern fog suppressors which have less effect on film speed.
The one most often encountered is benzotriazole which is
often found in developers using Phenidone.
Sulfite has a very complex function in a developer. It
tends to absorb oxygen preferentially to the developing
agents so protects them from oxidation from contact with the
air. It also has anti-oxident action with the reaction
products of development. These last are complex and vary
with the developer. For instance, the reaction products of
Metol tend to suppress development while those of
hydroquione tend to accelerate it. Where both developers are
used these two properties tend to counteract each other and
sulfite reduces them even more. Sulfite also has a "salt
effect" which tendst to prevent swelling of the gelatin.
This is important for several reasons but one important one
is that it tends to prevent the migration of individual
developed silver grains causing "grain clumping" and a
grainy appearance. Sulite has another very important
function and that is as a silver halide solvent. The solvent
effect affects the way the silver crystals form when
developed and tends to minimise grain. At the level of
solvent action present in developers like D-76 the action
also tends to slightly dissolve the surface of the halide
crystals making more development centers available to the
developer and increasing film speed slightly. More solvent
action, for instance as in full strength Microdol-X, will
destroy some of these development centers thus losing some
speed. There is an optimum amount of sulfite which depends
on the rest of the chemistry and on the intended use of the
developer. Sulfite is also present in fixing baths to
prevent oxidation of the thiosulfate and also to prevent
staining from carried over developer.
Liquid concentrate developers often do not have sulfite
but rather some other chemical which can be dissolved in
sufficient concentration but which functions as sulfite in
the active developer.
These four functions: developing agent, preservative,
accelerator, restrainer, are present in nearly all
developers. In a few cases sulfite is used as both the
preservative and accelerator (D-23) and the preservative and
restrainer are not always sulfite and bromide, as pointed
out above, and not all developers have a restrainer (D-76,
D-23 and others) but these four functions are present in
nearly all.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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