[rollei_list] Re: Rolleiflex 2.8C and two developers
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: "New Rollei List" <rollei_list@xxxxxxxxxxxxx>
- Date: Fri, 31 Jan 2014 22:47:14 -0800
Of course, this isn't exactly how T-Max RS works, because
the typical
dilutions do not extend conveniently. If standard dilution
is 1:4, to take
some of this solution and dilute it further to 1:9 is
inconvenient since it
isn't a direct ratio. Not to mention the fact that this new
dilution can
no longer be incorporated back into the original working
strength mixture
(especially since 1:9 is not a one-shot dilution, or at
least, doesn't have
to be). In other words, the normal practice is going to be
to mix the
entire bottle of concentrate at the same dilution, and keep
it that way.
This is Kodak being confusing 1:9 is the mixed stock
diluted to half strength. The "normal" working developer is
the concentrate mixed 1 part concentrate wtih 4 parts water
to make up the final amount. Total 5 parts. 1:9 is one
part concentrate diluted with 9 parts water to make up a
total of 10 parts or half strength. You can take the 1:4
mixture and dilute it with an equal amount of water to get
the same thing.
Kodak uses very old chemical terminology for their
dilutions. Most chemists would describe the 1:4 mixture as
1:5 meaning 1 part of the substance to a total of five
parts. The same thing is seen with, say, D-76 where we
typically say its diluted 1:1 to mean half stength, i.e.,
one part substance and one part diluent where most chemists
would call it 1:2 or one part substance to a total of two
parts.
Perhaps we should also introduce the term "concentrate"
This always refers to a liquid solution. The concentrate is
mixed wtih water to produce a stock or a working solution.
"Stock" solution usually also means a concentrated solution
that is not used directly for development or other
processes. An example is a print developer, say, Dektol.
Decktol comes as a poweder. It is mixed in a given solution
of water and brought up to a specified volume. This is a
concentrate although usually called a "stock" solution. To
use it this stock is diluted with some amount of water, in
the case of Dektol one volume of the stock to two volumes of
water, by Kodak terminolog 1:2, total three volumes. This is
the working solution. Some developers, mostly those in
powder form, are used directly from the mixed solution. They
may also be diluted but not always. Examples of such
developers are Microdol-X and Perceptol and D-76. Microdol-X
and Perceptol have properties that change when they are
diluted. These two, which are identical, are
extra-fine-grain developers. When diluted they lose their
extra-fine-grain property but deliver a higher film speed.
D-76 is often diluted half and half with water to obtain
reasonably long development times. Its chemical nature is
such that its characteristics when diluted are very little
different from the full strength solution. The full strength
solution of these developers is not strictly a stock
solution even though they can be diluted for use.
So, we have; concentrate, stock, working.
Anyway, I hope this makes things clearer.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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