U of S | Mailing List Archive | alt-photo-process-l | Re: Exposure times in tricolor gum

Re: Exposure times in tricolor gum


That makes a lot of sense.  If you test cyan, magenta and yellow inks from printers, the yellow is always by far the most dense to UV, with Cyan being far less dense and magenta less dense than cyan.

I'm not at all surprised that the pigments have the same effect.  Chris Anderson reported this to me a few years back when she started doing meticulous full color gum calibrations with PDN.  SHe also reported the yellow pigment layer having a very different curve.

Best Wishes,

Mark Nelson
On Nov 18, 2008, at 6:43:37 AM, "Henry Rattle" <henry.rattle@ntlworld.com> wrote:
From:"Henry Rattle" <henry.rattle@ntlworld.com>
Subject:Re: Exposure times in tricolor gum
Date:November 18, 2008 6:43:37 AM CST
Hi Loris,

My exposure times (50% gum/pigment, 50% saturated Potassium dichromate) are
7 minutes for C and M, 10 minutes for Y. These times are "standard printing
times" from precision digital negatives (PDN) testing, all exposed through
R255B60 colorised negatives, with separate curves generated for each colour.
(The C and M curves are very similar to each other, the Y is much flatter.)

Best wishes


On 18/11/08 12:20, "Loris Medici" <mail@loris.medici.name> wrote:

> This goes mainly to tricolor gum printers printing from digital negatives
> separately calibrated for each color layer: do you experience any exposure
> time variation? If yes, can you please tell me your exposure times (and
> dichromate strenght, only if it isn't kept constant) for each layer? I
> just want to see if there's a correlation / connection...
> I balanced the pigments according to 2Y + 1M + 1C. In other words, my Y
> stock paint:gum solution contains 2x paint compared to both M and C
> solutions. Using the same coating solution formulation (which is 1 part
> paint:gum solution + 1 part gum solution + 2 parts 10% ammonium dichromate
> solution), I find that yellow requires the most exposure whereas C
> requires the less (M in between). Is this similar in your case?
> Thanks in advance,
> Loris.