U of S | Mailing List Archive | alt-photo-process-l | Re: was Miracle size for gum now tonal range

Re: was Miracle size for gum now tonal range

Hi -
  It's been so long since I've written to the list....so long.
  I've two minor comments to add to the discussion.
  First, Gum, if I remember rightly, cures from the top down, thus the exposure must take into account the thickness of the gum layer, as well as the UV absorption of the pigment used.
  Secondly, I've found that the gum that stays on the paper depends in no small part on the gum located next to it, and so on and so on.  If one piece of gum is lost in development, the piece next to it is made more vulnerable and may go as well, despite the fact that it is properly developed.
  I've run some tests using dot screens, and have found that you can get much more latitude out of the print (a greater number of stops) by using the screen.  I believe this is due to the fact that every dot is an entity unto itself, and therefore doesn't affect the surrounding gum matrix.
  My 25 cents worth.  Good for a coffee in Turkey.  Best - Ed

-----Original Message-----
From: phritz phantom <phritz-phantom@web.de>
To: alt-photo-process-l@usask.ca
Sent: Sun, Oct 11, 2009 3:40 pm
Subject: Re: was Miracle size for gum now tonal range

hi marek, 
sorry, i can't offer these test strips either. 
i only tested the saturated dichromate (~25%) and 1/5th of the strength (5%) at double exposure. 
since i was going for maximum contrast for shadow exposures. 
i don't know if anyone else experienced the abrupt end of the curve in the highlights, but for me it looks like that there is a practical end to the linearity of the process, caused by movement in the water, which can never be exactly repeatable. 
also i think i've seen that small highlights in dark areas take longer to clear than bigger bright areas. a bit something like a chain reaction, one particle of gum going off and takes the next one with it. 
did anyone else ever see this? 
Marek Matusz schrieb: 
> SO actually 3 test strips should be compared. 

> case one 1x dichromate 1x exposure (your usual working scenario), it will 
> require shorter development 

> case two: 1x dichromate 2x exposure 

> case 3: 2x dichromate 1x exposure 

> I have done these and can not find the dfifference between cases 2 and 3, 
> now of course case one will show shot scale, because we have learned to 
> underexpose gum with thin negatives 

> WOuld somebody show me test prints of cases 2 and 3 showing any 
> difference? 

> I actually ruined my set by leaving them a bit longer for development and 
> then forgetting about them for a day, so I need to make another set for 
> show and tell. 

> Marek 

> > 
> <http://clk.atdmt.com/GBL/go/177141664/direct/01/