Re: Gum problem(s)

From: Yves Gauvreau ^lt;>
Date: 11/18/05-02:16:26 PM Z
Message-id: <04ab01c5ec7c$f47a4200$0100a8c0@BERTHA>

Not more tungsten then a photoflood Kate, the thing is that a gum dichro
matrix probably respond to light in a relatively broad manner with peaks and
valleys from relatively invisible UV light up into the visible light area
and I could say the same for most source of light but the peeks and valleys
would be more in the visible range. The exception would be laser which have
a very narroe spectrum. I asked the question earlier about this and the
answer was that the highest peek was around 350 nm which is in the UV range
and if I'm not mistaking it is just a bit below visible light (violet). I
suspect that a photoflood light gives out a significant peek in a region
where the dichro as also a peek maybe those corresponding peek are not as hi
as the 350nm one but I'm sure they are significant (hi) enough that the
dichro become insoluble which is what we are looking for. At 5 to 10 bucks a
piece they are a real bargain.

Based on what I've learned so far and if I can find out the level of
relative humidity that give the highest speed or shortest exposure time
using a photoflood bulb I don't think someone could convince me to use
anything else. I must add that I can use my shower to get the optimal RH
level, ain't this fun????


----- Original Message -----
From: "Kate M" <>
To: <>
Sent: Friday, November 18, 2005 2:37 PM
Subject: RE: Gum problem(s)

> But isn't photoflood a tungsten light source? There would be very little
> output then, a lot of heat though.....when ever I've done copywork under
> photofloods, I've used tungsten film.
> Kate
> -----Original Message-----
> From: Katharine Thayer []
> Sent: Saturday, 19 November 2005 4:31 a.m.
> To:
> Subject: Re: Gum problem(s)
> Yves,
> Thanks for description.
> Okay,, this sounds like (1) pigment stain (not clearing in masked
> areas) and ... (2) ... hmmm, I'd need to see the print, I think. Your
> description of not much pigment in exposed areas sounds like
> underexposure, but 20 minutes under a photoflood is a very long
> exposure. My exposures are from 1 to 5 minutes with the same kind of
> light; most exposures are 2 or 3 minutes. But if you live in a very dry
> climate, you may need a longer exposure, as there is almost a vertical
> inverse relation between humidity and time required for hardening.
> Katharine
> On Nov 17, 2005, at 6:30 PM, Yves Gauvreau wrote:
> > Hi all,
> >
> > I tried a few variants in the pigment / gum ratio and coated to
> > different
> > tickness directly on paper using various exposition times. None of the
> > combination I've tried cleared to the paper in masked areas. Also I
> > tried
> > this with one dark brown watercolor paint tube and one using a dry
> > pigment
> > (dark brown also). I use a 1:1 ratio of pigment/gum and saturated pot.
> > dichromate solution.
> >
> > 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.
> >
> > 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.
> >
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Received on Fri Nov 18 14:15:09 2005

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