Re: was Miracle size for gum now tonal range

[phritz phantom <phritz-phantom@web.de>]

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
>
> __________________
>
> Christina Z. Anderson
> http://christinaZanderson.com/
> __________________