Re: was Miracle size for gum now tonal range
Yes, phritz, this observation corresponds with mine and with the
observations of observant gum printers through more than a hundred
years; more dichromate= a longer tonal range (more steps), less
dichromate= fewer steps and a more contrasty print. And I think
you've got the right idea, at least part of it, for why that's so.
See, you aren't at complete odds with gum at all, even though it
feels that way at the moment; you do have a sense of how it works.
Katharine
On Oct 10, 2009, at 1:02 PM, phritz phantom wrote:
hi chris,
i did tests for tonal range about a year ago and again two months
ago. i printed step wedges with saturated and 5% ammonium
dichromate. since i don't have a proper step wedge (yet), i can't
say how many steps, but for me i get about twice the tonal range
with saturated than with 5%.
with the (uncurved) chart throb scales and 5% am-di there appr,2.5
lines between max. densitiy and white. while with the saturated
solution there are 5 or 6 lines between white and black.
another thing i noticed is that the 5% solution does significantly
clear better than the saturated (on the cheap paper i use). i
wouldn't really call it stain, but the whites of the 5% sheet are
noticably more brilliant. also i think the tonal range of the 5%
does break off more abrupt in the highlights. maybe it's just the
fine highlights that wash off quicker in the development, because
of the lesser light sensitivity of the 5% solution.
phritz
Christina Z. Anderson schrieb:
Loris,
Someone said in the literature recently that gum prints 2 stops
(log .6). I was surprised at how low this was, as I always hedge
my bets and say 4-6 stops, with 6 a stretch. Partly if you don't
clear with pot metabi you can get a false read of maximum black
because the brown stain of the dichromate can read a darker step
when it is not really hardened anymore "goo" on top. So I always
figured that the 2 stop person cleared and found that to be true.
Or maybe was guessing it from the seat of his/her pants.
But it's all kind of a moot point I suppose once you fit your
negative curve to the exposure/dichromate you use.
I use a 15% solution of am di (2 tsp to 100ml quick n' easy
approximate).
So Marek is figuring a 3 stop range, you a 4-5 stop range....
You say that with weaker di and greater exposure you are getting a
longer tonal range--do you have a picture on the web of that
comparison somewhere?
Chris
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Christina Z. Anderson
http://christinaZanderson.com/
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