hi,
are there any film developers that rely only on the tanning aspect of catechol and not its staining property? thanks
thank you Sandy,
can i infer from your statement that increasing the sodium metabisulfite upto 4x won't affect the staining properties?
Sulfite or metabisulfite, bisulfite that is.
What's it going to be? Dan
But what is a benefit of tanning vs.. staining ? wouldn't it have similar result in the end when printing?
IA
Not necessarily. Staining adds a dye that increases contrast. Tanning prevents development spread and increases resolution. A tanning but not staining developer might be preferred in some cases.
Sandy King
this stopping of development spread IMO is one of the greatest attribute of a tanning dev.
Its what sold me on pyro in the first place.
Sandy could you go further into the way a tanning dev stops the spread , I think that this is the most underrated aspect of pyro.
With a tanning developer there is very little migration of silver halide during development because early in development a hard relief image is formed. This results in more precise reduction that minimizes infectious development (spreading of silver development beyond the exact image boundaries).
You can see the result if you make two negatives of a strongly back lighted scene, say a tree in the winter with no leaves against the sun. Develop one of the negative in a traditional developer, the other in a pyro type developer (PMK, Pyrocat, etc.) and compare the results. Chances are there will be a lot less infectious development with the pyro developed negative.
Some years ago I carried out some resolution tests comparing two pyro type developers (PMK and Pyrocat-HD) with two traditional developers (D76 and Xtol). With every film tested the pyro developers gave about 15% higher resolution. The statement that Pyro developers are sharper is not a myth, but a fact that can be tested and proven.
Sandy King
Not really much of a distinction for this purpose. Sandy King
Your post 2 this thread mentions upping the sulfite by 5 - 10
times. The result a tan rather than a stain. And it matter
little if it be sulfite or bisulfite? Dan
do the rules change in two bath development? for example,
bath A
Metol 2.5g
Sodium Metabisulfite 10g
Pyrocatechin 5g
Water to make 1 litre
bath B
sodium hydroxide 10 g
water to make 1 litre.
do you think that it will stain because of the low amount of bisulfite absorbed into the gelatine? i've used your ratio of bisulfite/water assuming that you found a balance between enough bisulfite to prevent oxidation but not enough to interfere with the formation of the stain. obviously, one of my driving interests with this formula variation of your pyrocat m is to extend the longetivity of bath A. your thoughts are much appreciated Sandy.
... bisulfite in the stock will become one mole of sulfite in the
working solution when the stock is diluted with water.
... when a stock solution containing either is mixed with water
to form a working solution the bisulfite or metabisulfite is
converted to sulfite, one mole of bisulfite to one mole of
sulfite, one mole of metabisulfite to two moles of sulfite.
Simply adding water will not convert a bisufite into a sulfite.
A bisulfite is an acid salt where a sulfite is a normal salt;
in this case both are salts of sodium.
As for sodium metabisulfite and it's conversion to sodium
bisulfite: Na2S2O5 + H2O > 2(NaHSO3).
The normal salt is mildly alkaline, about ph 10, while the
acid salt is mildly acidic, about ph 4 Dan
So we could get there by adding 5X sodium metabisulfite to the stock solution, or 10x sulfite directly to the working solution.
Sandy King
I can not say for sure how long it will take the sulfite to break down in a 1:10 working Pyrocat-HD solution but you could run a quality control test at Day one, Day 7, and Day 14 and 28 to check it.
Anyway, I guess there are two main questions. The first is how much sulfite is too much such that it kills the stain? And the second, once the correct amount of sulfite is determined, how long will it preserve a working solution? I am going to suggest a maximum of about 5X the amount of sulfite.
Sandy King
Sorry for being ignorant:
Working solution? as an A+B+water? Dump 10x bisulfite in it and develop?how many times can you work with this working solution?
Would the developing times be cut in half, what would you recommend for a starting point? would it still be fine for DBI without the stain , but with tan?
If you were working with PyrocatHD with this additional bisulfite , say 4 batches(10sheets each) of film ,could you possibly use same working solution for all 4 batches ?
I would not care to keep working solution for a week at a time , but it would be handy and less wasteful if it could be reused in a matter of a few hours
Thank you.
IA
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