Re: D-76 to Lc-1

[Richard Knoppow <dickburk@ix.netcom.com>]

At 11:01 AM 08/01/2001 -0600, you wrote:
>Hi:
>
>I'm an avid using of Dave Soemarko's LC-1 developer.  I did some reading
>on developers and looked up the formula to d-76 and comparied it to lc-1.
>
>Below is my understanding of the chemistry involved.  Would some real
>chemists clarify this?
>
>D-76 and Lc-1 have very similar ingredients and concentrations.  The main
>difference is D-76 has Borax and lc-1 has sodium bisulfite.
>
>These two ingredients are used to set the pH of the developer.
>
>D-76
>
>Water (125F/52C)              750 ml
> Metol                         2g
> Sodium sulfite (dessicated) 100g
> Hydroquinone                  5g
> Borax                         2g
> Cold water to make          1000ml
>
>LC-1
>
>Soemarko LC-1: Stock A
> water                 750 ml
> metol                 3.0 gr.
> sodium sulfite       60.0 gr
> hydroquinone          3.0 gr
> cold water to make    1.0 liter
>
>Soemarko LC-1: Stock B
> sodium bisulfite     10.0 gr
> water to make         1.0 liter
>
>
>Borax is used to make the pH of D-76 alkaline.
>sodium sulfite is used to make the pH of lc-1 somewhat acidic.
>
>Dave has lc-1 made from two solutions.  Mixing A&B&water in different
>proportions changes the pH of the developer which changes the "contrast"
>of the developed negative.
>
>Developers need an alkaline environment to work well.  Dave made LC-1
>somewhat acidic to retard the activity of the develop in order to make it
>a very slow acting low contrast developer.
>
>I am wondering if it is possible to add something to D-76 to make it more
>acidic and thus make it act more like LC-1.  Changing the pH of LC-1
>doesn't change its ability to develop negatives.
>
>Would it be possible to add an appropriate volume of, acetic
>acid - stop bath, or sodium bisulfite, to D-76 to lower its pH and have it
>work like LC-1?
>
>I believe borax acts as a buffer and tends to minimize pH changes within a
>certain range.
>
>Would the addition of a small volume stop bath alter anything but the pH?
>If not could this be used to convert d-76 to somehting like lc-1?
>Everyone should be able to get stop-bath and D-76!
>
>If this were possible people without access to metol could make their own
>low-contrast version of d-76.
>
>I have dim memories of an equation used to calculate the pH of solutions.
>Maybe this could be used to figure out the pH of a particular LC-1 mix,
>and then used to calculate how much stop bath would have to added to a
>particluar volume of D-76?
>
>Does anyone have an idea of whether or not this would work?
>
>Gord
>
>
  D-76 is an interesting developer. Its probably been analysed to a greater
extent than any other. Partly because it was the first borax fine grain
developer and partly because it became the defacto standard developer for
the motion picture industry for decades. 
  In 1929 H.C.Carlton and J.I.Crabtree, of Kodak Research Labs published a
paper describing a buffered form of D-76 and descriptions of about twenty
variations of the formula. The reason for the buffering is to stabilize the
activity of the developer. 
  I was discovered shortly after the announcement of the formula (devised
by John Capstaff of Kodak) in 1926, that the activity rises slowly due to a
slow increase in pH. Carlton and Crabtree did not know what was causing
this pH rise but decided a strong buffer system would counteract it. Their
solution was to increase the amount of Borax by four tims and buffer it
back to the pH of fresh D-76 with Boric acid. The pair are an effective
buffer system.
  When equal amounts of Borax and Boric acid are used the developer has the
same activity as fresh D-76. Carlton and Crabtree also show that the
activity of the developer can be varied over a rather wide range by
adjusting the ratio of the two buffer components. This was an advantage for
motion picture processing in fixed speed machines since negative contrast
could be varied independantly of development time. 
  Carlton and Crabtree show a chart tracking gamma vs: time of development
for a period of 49 days. The time needed for unbuffered D-76 to reach a
given gamma after 49 days is little more than half the time needed by fresh
D-76. The times for the buffered version are the same within experimental
error.
  Current packaged D-76 is the buffered version.
  Ilford has adopted the buffer system for Microphen. Microphen is a
Phenidone version of D-76.
  Sodium bisulfite or potassium metabisulfite is used as a pH adjuster in a
few developers. Kodak D-61 is an example. This is a fairly powerful
carbonate accelerated formula mainly intended for photofinishing. It has
been obsolete for some years. 
  Metol has the somewhat unusual property of developing in neutral or
slightly acid solutions. Amidol is the only other reducing agent which will
work in an acid environment. 
  Kodak D-25 is an example of a neutral Metol developer. This formula was
developed (no pun intended) from D-23 by adding 15 grams/liter of sodium
bisulfite. The resulting lowering of activity, and consequent lengthing of
development time, results in very fine grain silver because of the
relatively long period the sulfite has to act as a halide solvent. 
  In the paper introducing D-23 and D-25 it is stated that the activity of
the developer can be varied by adjusting the amount of bisulfite. Reducing
it results in faster development, less loss of film speed, and coarser
grain, until no bisulite is used (D-23) where characteristics are similar
to D-76.
  In low pH developers like D-76 the Hydroquinone is inactive as a
developing agent. Hydroquinone requires a threashold pH of about 10 to be
active. D-76 is about 8.9. The Hydroqinone does, however, have an important
function, namely to regenerate the Metol. Even though D-23 has development
characterists similar to D-76 its capacity is much less. It also has
somewhat different edge effects when diluted since these depend on
developer reaction products. D-76, even diluted, has less tendency to
produce edge effects although, at 1:3, it will produce substantial acutance. 
  Dave Somarko's developer appears to be something like D-23, diluted 1:1,
with Hydroquinone added, and adjusted neutral or slightly acid pH with
bisulfite. 
  Because of the relatively low amount of sulfite it may not have the
extra-fine-grain effect of D-25, but may approach it, and should not
depress film speed quite so much. I am not sure what effect the
hydroquinone has since it is inactive. It may affect edge effects as it
does in D-76.
  There is a good section on fine grain developers in _Modern Photographic
Processing_ Grant Haist. This is long out of print but reprints can be
obtained from the author, Grant Haist, P.O.Box 805, Okemos, MI, 48805
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com