hello, Just want to Thank everybody who contributed an answer to my problem concerning AZO. Very helpful. Just have to get some Amidol from my photo chemist. Somebody mentioned that precautions had to be taken with Amidol. Could precisions be made concerning the precautions to be taken when using Amidol. Do I have to wear a Hazmat suit ;)
Cheers, Bogdan daniel wrote:
Hi,Just to add my point. I have noticed that fogged papers ( for exempla old Kentemere Kentona) can be used for Lith printing with Lith developers without fog. The borders are pure white. If of any help for lith printers.Daniel Bouzard Richard Knoppow a écrit :----- Original Message ----- From: richard lahrson To: pure-silver@xxxxxxxxxxxxx Sent: Wednesday, May 20, 2009 6:42 PM Subject: [pure-silver] Re: AZO and Benzotriazole for anti-fogging Hi! I've used some Azo that had not been used in decades and ii prints great. I understand that the silver chloride papers may keep better than sillver bromide. Perhaps the slower chloridecrystals fade slower? The box of Azo is 2 1/2 square size, perfect for any square 120 image! Best. RichOn May 20, 2009 3:20 PM, "Bogdan Karasek" <bkarasek@xxxxxxxxxxxx> wrote:I'm not a chemist and have learned that photographic chemistry is exceedingly complex and advanced although one can get a rough idea of how things work. I don't know for sure why some papers and films have longer shelf life than others but in general the slower the emulsion the longer it will last. It may be that silver chloride doesn't degrade as fast as silver bromide or combination emulsions but there are so many factors involved that that sort of very broad statement may not be true. At least part of the fogging is caused by a continuation of the ripening process during which the emulsion gains in speed. While substances are added to stop this process when it has reached the desired point it does continue to some degree. The result is the generation of silver halide crystals that develop even if not expososed to light. These are the fog crystals. Anti-foggants like Benzotriazole or potassium bromide tend to suppress development of these particles more than weakly exposed particles so they reduce the amount of fog. As more anti-foggant is added some of the more sensitive halide particles are affected thus reducing the speed of the emulsion. For negatives light to moderate fog adds density uniformly so that it does not affect contrast only overall density. Using anti-foggant here serves little purpose. For paper the fog veils highlights, which is undesirable, so enough must be used to maintain clear highlights. Anti-foggants can also affect the morphology (shape) of the developed silver crystals and, thus, the color of the image. Bromide tends to produce fine grain particles which usually tend toward yellow, and Benzotriazole tends toward blue. However, the amount of change, if any, depends on the emulsion and developer. Benzotriazole works best at moderately high pH. Some developers, notably Phenidone and its derivitives are not very sensitive to bromide so benzotriazole is used in developers containing them. One also finds both in many developers. Micheal's point about the amount of bromide to use is well taken. A minimum amount is necessary to prevent highlight veiling in most print developers but much more can be added, the amount depending on what looks right. Note that the use of bromide is usually supposed to make prints tone more warmly but Ansco had a patent on using very large amounts of bromide to make indirect sepia toner cooler. (Will find this and post the patent number).-- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there. --------------------------------------------------------------------------------------- Orange vous informe que cet e-mail a ete controle par l'anti-virus mail. Aucun virus connu a ce jour par nos services n'a ete detecte.============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.
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Bogdan Karasek
Montréal, Québec bogdan(at)bogdanphoto.com
Canada www.bogdanphoto.com
"I bear witness"
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