Why Pyrol rather than hydroquinone?

[dancqu]

Perhaps the high density of the lith image
makes the stain not noticable.

Just what I was thinking possible. Many years ago I did
process camera work and half tone processing. I was not
looking for color then but on reflection do not recall any.
Those little dots are small and/or compressed and all
very dense.

The little lith printing I've done shows the dense portions
to be black, warm at best, while any less dense areas shade
from light tans to very dark browns; at least with my
homebrew lith. Dan

[dancqu]

[QUOTE=sanking]
"For whatever it is worth."

I can only wonder what is going on with that hydroquinone.
That 2 grams/liter is also a Lith developer sulfite maximum.
Reconcile, if you will, HQ's oxidation products giving lith
development and at the same time those oxidation
products being involved in tanning gelatin.


I've given that above some additional thought. On reflection,
when working with my lith surprise brew, I saw that the
image tanned brown as it emerged. After several minutes of
slow increase in density a rather fast increase took place.

Hydroquinone initiates the reduction of the silver halides and
the semiquinone is produced. The semiquinone is consumed
by the gelatin, that being tanned. Hydroquinone MAY be
regenerated at that time. Quinone though, necessary
for infectious development, is NOT produced.

After most of the tanning has been done the semiquinone is
free to oxidize to the quinone and infectious development
takes off. All that with low sulfite levels.

But what if sulfite levels are high? Nothing happens; perhaps
a faint image. Interesting. By that I'd conclude that more
than a very little sulfite will maintain a regenerated
hydroquinone.

Likely the level of sulfite mentioned, 2 grams per liter, may
vary some and one still expect a tanned, lithed print. Dan