[rollei_list] Re: OT:Photographic Chemistry
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 23 Feb 2010 00:36:47 +0100
Yes Richard, in the bibliographic references page I had mentioned you
can also read: "Mason, L.F.A., Photographic Processing Chemistry,
Focal, London 1975. This book can serve as an update on Glafkides."
Anyway Glafkides contains the fundamentals of the photographic
chemistry, the way every developer, developing agent and fixer element
works alone and in conjunction with other elements and has practical
procedures for different items, the book is old regarding new formulas
used today and in fact it does not contain B&W negs developers
formulas very much, but he explains the way the elements work and all
about the film (and other materials like paper) developing theory, the
"latent image", the "image germ" etc. and I'd bet you could "invent"
your own developer following his explanations after a bit of practice.
The D-76 formula he mentions is the current D-76 formula.
Carlos
2010/2/22 Richard Knoppow <dickburk@xxxxxxxxxxxxx>:
>
> This is an often cited text but its getting old. D-76 was described as a
> fine grain developer when it was first published. It dates from 1926 and was
> originally described in a brochure for a then new fine grain duplicating
> film for motion picture negatives. It was soon adopted as the standard
> negative developer by the motion picture industry. It has probably received
> more study than any other developer. The formulation was worked out by John
> Capstaff, of Kodak Laboratories, who was also pretty much the inventor of
> 16mm home movies and practical reversal processing.
> After being in use for some time it was discovered that the original
> formula increased in activity with time. It was determined that the pH went
> up and the cure was described in a very extensive paper published by Carlton
> and Crabtree of Kodak in 1929. They used a formula which had the addition of
> sodium bisulfite as a buffer to maintain a constant pH. The actual cause was
> not discovered until the 1950s!. It turns out to be a slow reaction between
> the hydroquinone and the sulfite which produces just enough sodium hydroxide
> to raise the pH slowly. The current packaged D-76 appears to be the buffered
> variety.
> The developers in use at the time D-76 was devised were mostly pyro based
> and others with sodium carbonate as the accelerator. One reason that D-76
> has relatively fine grain is its high salt content and moderate pH. Both
> tend to prevent undue emulsion swelling and consequent grain clumping. The
> high sulfite content also affects the shape of the developed silver
> particals tending to a "filamentary" form which has higher covering power
> than the simpler form produced by low solvent developers. The solvent effect
> of the sulfite also acts to expose more development centers which increases
> film speed a little.
> Developers of the D-76 type tend to produce a low level of overall fog
> when used the first time. If re-used the bromide accumulated from the film
> will reduce the fog level but also tends to reduce speed and shadow detail
> just a little. Carlton and Crabtree found that a small amount of bromide
> added to the fresh developer would suppress the fog and result in a slight
> increase of film speed. They used 0.25 grams/liter.
> There are an enormous number of formulas based on D-76, virtually every
> film manuacturer had some variation. It turs out that 100 grams/liter of
> sulfite is probably a bit too much, 80 grams/liter is closer to optimum.
> The hydroquinone in D-76 is virtually inactive as a developer because the
> pH is too low. However, it acts as a mutual preservative and regenerating
> agent with Metol so that the capacity of D-76 is greater than if it is
> omitted.
> A more recent book on photographic chemistry was written by Grant Haist,
> late of the Kodak Research Laboratory. It is long out of print but Haist
> himself republished it in a well printed hard cover edition. I am not sure
> Haist is still alive but a web search might find him. He lives in Okemus
> Michigan.
>
> --
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
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