Now I know latensification probably isnt widely used any more because
of the deveopment of high quality high speed black and white emulsions.

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?