You say :
"K.... indulge a relative beginner (in gum): are we talking about a 1 to 6
hour wash after all the printings and a clearing bath?? If not, wouldn't
the entire exposure simply wash off?? Or am I missing something here? "
No, although it might appear to be the logical result, if you have got the
exposure right and you have allowed the light to fix the finished gum, you would
have to soak it for months before the gun became even soft enough to scratch off
the surface. The point of the leach/wash is to wash out the soluble dichromate
from the porous gum.
"Secondly (perhaps out of this threads discussion): Can someone explain to
me the "correct" way to determin density range with a step wedge. I (in my
isolation) have been taking my zone 8 value (very light greys with just a
"touch of detail", say it is step #13) and subtracting my step 2 value (as
dark as I can get and still hold a "touch of detail", say it is step 3). I
then take step 13 minus step 3 equals 10 steps or 5 stops. It works for
me, but is this standard??? Obviously, I've consentrated on the zones at
the threshold of detail, but some things I've read suggest that zone 1-9
(threshold of tone) might be the intenational standard?? I may soon be
teaching, and I've never understood if my method matches the rest of the
world.
I had a brush with a very real application of this principle last week. My usual
practice is to measure the range from first perceptible tone to maximum density
with that measurement being related to base plus fog. Each two steps being a
stop.
Somebody had prepared some positives for me which were supposed to have the same
density range. But the range had been measured from base plus fog rather than
first perceptible tone which in some cases was a difference of about half a
stop. I should have made my own measurement of the density range before starting
work but as I trusted the work of a fellow professional, who did not realise the
very real significance this difference can make, I wasted a week before I
realised what was going wrong.
But in general I think that Peter Marshall is probably the best person to
comment on step wedges.
Terry King