Curves yoyo for Platinum on PPE

Hi - I am working on a new curve for a Pt/Pd print-out process. I am yoyoing endlessly between a bright curve and a dark curve.

The curves are good, smooth curves, but each time that I make a new target and take measurements, and create a new curve in the PPe tool, that resulting curve overshoots.

So if I begin with a curve that looks bright, the next curve makes a target that is too dark overall, and the next one is again too bright. etc.

I am using a lot of chemistry to do this.

Question: would it work if I just took two curves and made an average of them using a spreadsheet? Presumably only if the curves are nice smooth curves with opposite differences from the linear at all points. It would not be totally elegant but it could be a workaround.

Is there a different way to do a gradual reduction in negative density from the bright pirnt using some other technique in the PPe tool, rather than using the curve that PPe generates?

Many thanks,

I’ve gone through a few spells of this when working in collaboration with other people coating the paper and/or controlling the darkroom variables. Over time it slowly dawned on me that the over-under thing was cause by physical variables name these two biggies.

  1. Humidity and paper dryness and coating changes from print to print.
  2. Not letting the neg dry for the exact amount from one target to the next.

These two things can do all the swings you’ve witnessed. After we regulated our darkroom (we use de-humidifier, humidifier, AC unit, and we dry the negs in the print dryer for 1 hr, and we hang the coated paper and expose it the MINUTE it has hung for a set amount of time) all the swings disapeared.


Thanks - that’s really helpful.

I have a couple of follow up questions:

  1. Does the negative get more dense or less dense, the longer the drying time.

  2. Do you recommend that paper is left to dry for a period after coating, before it is placed into the humidity chamber? I am currently coating the paper, leaving it in a box for 5 minutes, and then placing it into a 74% humidity chamber for 90 minutes before exposing.