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

Re: Exposure times in tricolor gum

Thanks Henry,

By "...Y is much flatter..." you mean that it's closer to the ideal 45
degrees linear transfer function or it's more drastic? I'm currently
printing using a single curve devised from M tests.

What can you say about the pigment concentrations you use?


18 Kasım 2008, Salı, 2:43 pm tarihinde, Henry Rattle yazmış:
> 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
> Henry
> 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.