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#1
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Latensification with Hydrogen Peroxide
Now I know latensification probably isnt widely used any more because
of the deveopment of high quality high speed black and white emulsions. I thought my little break from this forum was good enough to show eveyone that I don't fool around. I was hoping to do some snip tests with hydrogen peroxide post-exposure latensification. The only other methods I found any information on was the use of mercury vapor, ammonia, and ammoniacal silver chloride but these are far less pratical because of their toxicity. Latensification is basically a slight increase in base fog to increase the effective film speed. Each silver halide needs about 6 photons. If a silver halide is only hit with 3 or 4 photons then flashing it briefly with light or exposing it to hydrogen peroxide will build the latent image before introducing the developer. I figure I'll take a roll of neopan 100, shoot a frame with a gray card at iso 50, 100, 200, 400, 800, 1600 and 3200, then do a prewash of water, use hydrogen peroxide (either 3% or 1% whatever the drugstore sells) for about 3 minutes then increasing development 10% to make up a little bit for the lost in contrast from fogging the base. I figure I'll take a base fog reading on a densitometer and subtract it from the reading of the gray card on each frame to figure out what iso it's effectively being pushed to. Another method I've learned of was post development hydrogen peroxide steaming. I've heard this has been used on Fuji neopan SS 100 (now replaced by Acros) to suscessfully push it to 1600 by exposing it to hydrogen peroxide (3%) vapor at 105F after a 2 stop push development and before fixing. I think this method is more akin to change the development rate in highlights and shadows, but I dont know. I found this quote in another photography forum about it: "I suspect the mechanism is a combination of heat promoting rapid additional development in shadow zones, and peroxide promoting rapid exhaustion and oxidation of developer in highlights, to produce an extreme compensation effect and effectively push the shadows another stop or more beyond the basic 2- or 3-stop push (which gains 2/3 stop in the shadows, max) given before the peroxide treatment. There may also be a component of preferential oxidation of developed silver in the highlights, but silver oxide wouldn't fix out (I don't think), so that's not the whole story. Also worthy of note is that silver is one of the best catalysts for decomposition of peroxide into water and oxygen, I'm sure this enters the equation somewhere." Now I think in the first method the hydrogen peroxide is hypersensitizing the film to a point by increasing its effective speed. The second method I bleieve is using the break down of hydrogen peroxide to reoxidize developed silver. Has anyone had any experience with either of these two methods? Or can anyone at least clear up some of the chemistry for me? |
#2
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Latensification with Hydrogen Peroxide
"I thought my little break from this forum was good enough to show
eveyone that I don't fool around. " sorry about that, I copied and pasted this from another forum I posted in where there were some rude members. Just disregard that sentence. |
#3
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Latensification with Hydrogen Peroxide
Yep, there are no rude members on this forum.
On to the post, no reason why you couldn't shoot three rolls at the same range of bracketed exposures, process one normally, process one with pre-development latensification and one post-development latensification. -- darkroommike wrote in message ups.com... "I thought my little break from this forum was good enough to show eveyone that I don't fool around. " sorry about that, I copied and pasted this from another forum I posted in where there were some rude members. Just disregard that sentence. |
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