Re: Exposure times in tricolor gum
Yes, the Y curve is quite a lot closer to the 45 degree line - less sigmoid
than the cyan and magenta curves, which are close to identical.
Afraid I mix the pigment by eye - small blob, larger blob... So can't be of
much help there.
On 18/11/08 12:50, "Loris Medici" <firstname.lastname@example.org> wrote:
> 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)
>> 7 minutes for C and M, 10 minutes for Y. These times are "standard
>> times" from precision digital negatives (PDN) testing, all exposed through
>> R255B60 colorised negatives, with separate curves generated for each
>> (The C and M curves are very similar to each other, the Y is much
>> Best wishes
>> On 18/11/08 12:20, "Loris Medici" <email@example.com> wrote:
>>> This goes mainly to tricolor gum printers printing from digital
>>> separately calibrated for each color layer: do you experience any
>>> 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
>>> 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,