WAS Re: gloy for tricolor on yupo? IS gum printing exposure

Katharine said:
> Well, of course, all of this goes without saying: for each combination
> of light, dichromate, film, paper, etc etc there is a "best" exposure,
> which can easily be determined with a step wedge, and which produces the
> optimal hardening of the gum layer; anything less than that exposure
> will result in less than optimal gum hardening. I would be very
> surprised if there are any gum printers who don't know that.
>
> But my point, which I wonder if you've missed, was that this "best"
> exposure is different for every system of equipment, materials, etc.
> It's hardly surprising that your students found that the same exposure
> worked for them, given that I would assume that they would be using the
> same equipment and materials, but surely you're not suggesting that 6
> minutes is an optimal exposure in some kind of general and absolute
> sense.
> Katharine

Katharine,
How could I possibly miss a point you make, you make them so clearly and
thoroughly?

(See, I changed the subject line, above.)

I have never suggested that 6 minutes is an optimal exposure in an absolute
sense, and I would be very surprised if there are any gum printers who don't
know that. I don't think Loris or I would assume an alt list reader would
jump to that conclusion when reading Loris' post.

That said, if I know someone is using a UVBL light source I would certainly
share with them my personal exposure time to get them in the ballpark.
Which I do, and I did, and it's a pretty sweet time at that. In fact, I
think Sarah Van Keuren and/or Ernestine Ruben got me in that ballpark in the
first place.

It was not come upon lightly, either: I took every blue, yellow, and
magenta pigment I have and exposed them at 3, 4 and 5 minutes (after
previously exposing every single pigment I own at 1,2,3,4,5,6 minutes).
After a hundred Stouffers, and, with different strengths of dichromate, too,
I still settle on that time with UVBL. But, 5 minutes is OK, too, except I
tend to be a bit rough with my gums and don't want to worry about a layer
being tenuous.

Yves, the PDN system takes into account the UV density of the substrate.
Pictorico is about 1/2 stop, and you can also overlap the substrate of
choice with the step wedge when exposing. Stouffers knows the density of
their step wedges and those with UV densitometers for us alt process freaks
also know that data. In gum printing the density of the Stouffers itself is
negligible, but I do take into account the Pictorico.
Chris
Received on Fri Mar 31 08:48:42 2006