Re: Gum problem(s)

On Thu, 17 Nov 2005, Yves Gauvreau wrote:

> I also notice the unmask area don't hold much if any pigment either. It's
> like some pigments get into the paper causing a noticable darkening and
> almost none stays on top of the paper in insoluble gum. My last attempt was
> 20 minutes exposure under a #2 photoflood light.
>

20 minutes under a photoflood could cook (ie insolubilize) your emulsion,
unless you aim a fan on it. For what it's worth,in my experience,
photoflood is lousy for gum...

My suggestion would be use a 21 step wedge, because what you're doing now
is by guess & by golly. Then you make the negative to correspond to the
steps you are actually printing... But measure your emulsion carefully --
by drops of gum, of water & of dichromate solution, plus weight of paint.
You don't have to do this perennially, once you get the ballpark you can
estimate, but now you're flailing. Suggestion: start with 20 drops gum, 20
drops dichromate & 20 drops water, and a pea sized bit of a nice easy tube
color -- what brand have you got?

For the purpose of zeroing in on exposure & formula, opaque or transparent
paint is fine -- but... it's got to be a paint that works. Some in some
makes can be exceedingly difficult (as I've always found, in most combos,
carbon black). Which are you using?

J.

> Any suggestion on what is the problem(s) and what I should try next?
>
> Thanks
> Yves
>
> PS Both pigments I used seem to be of the opaque type if this could help.
>
>
Received on Thu Nov 17 22:48:15 2005