Re: Gum problem(s)

From: Tom Sobota ^lt;[email protected]>
Date: 11/18/05-10:13:33 AM Z
Message-id: <>


I'm not Judy, but if you allow for an additional opinion ...

In the first place, 11.5ml of mix seems to me way too much for covering
a 5" x 7" sheet. Or you perhaps use this quantity for coating several

Second, 1.5ml of pigment is also a suspicious quantity, because you
don't say how much of this is dry pigment and how much is Photo-Flo.
I use dry pigments, and the quantity varies wildly with the covering
power of each pigment. Earths such as burnt sienna, raw umber or such
cover much less than, say, the quinacridones.

In general, as they say, you should still be able to read newspaper font
through the coat, albeit with difficulty. This is perhaps not an absolute
rule but it is good enough for a start. It assures you that the coat allows
the passing of light, at least twice. Should you need more density, you
can always later attempt multiple coats.

As an example (not to be taken as words of wisdom written on stone):
I use some 200mg of Winsor & Newton Indian Red (red iron oxide)
to cover a 24x30cm sheet of paper sized with two coats of gelatine
hardened with formaldehyde. I don't use the same paper as you do
because, as has been previously discussed, it is not available in Europe
but several members of this list swear by that paper so it must be good.

Do you size your paper? I don't really recall if this paper is used with
or without sizing by those that use it.

Photoflo is a good idea when working with dry pigments. I use Agepon,
the Agfa equivalent, but any surfactant agent should help. Only I use
it in minimal quantities: just a very small drop which is enough to
break the superficial tension of the gum+dichromate mix. Perhaps
you are using too much Photoflo?

I have no experience with the kind of light that you use, so I cannot give
an opinion. Do you have sunny days where you live? If so, why don't
try some clear-sky exposure? This is guaranteed to have enough ultraviolet
content for your needs, mostly between 10am and 3pm or so. But avoid
the direct sun!

The uniformity of the coat, within some reasonable range, is not that
important at first. You will have time to perfect your coating technique
later, should it be necessary and should you still be hooked with gum :-)

Good luck

At 14:59 18/11/2005, you wrote:
>For my first tries with the photoflood I used it in a 10" reflector and the
>paper got a bit warm if not hot but for this last try I used it without a
>reflector and there was insignificant warming as far as I can see.
>To show that what I did may not be as bad as I suggested I could join a scan
>of my last try if this is aloud here. (I'll send it directly to you so you
>can see for yourself)
>Here are the details of setup I used with some observations and some
>5 ml of Gum solution (1 table spoon of powder with 30ml of deionized water
>which is about a 1:2 ratio)
>1 to 1 1/2 cm of pigment paste I mix from dry pigment and photo flo 200 (I
>didn't measure but I didn't use more then 1.5ml)
>5ml of saturated potassium bichromate solution ( used good water here again)
>I coated very thinly a 5" x 7" Fabriano Aristico extra white ( grana satina
>hot pressed) 100% cotton and 140/300. I could add that my coating wasn't
>that uniform either I think it shows in the image I've attached.
>Exposed 20 minutes under a #2 photoflood light (no reflector).
>Develop in 3 bath at ~ 68F ten minutes in each (with no agitation except for
>a peek at about 5 min for the first 2 baths).
>I notice that the pigment/gum in the area outside the step tablet was
>extremely soft and I removed it all by rubbing my finger as delicately as I
>could. I assume I shouldn't do that in the future. One may say that's very
>good, you got 7 to 9 steps showing to which I would reply the separation
>between those step is close to inexistant and we can hardly read the number
>or text because of the texture and staining.. If this was a delicate flower
>with lovely details, only my imagination could tell and this is certainly
>not what I was expecting but I also saw in my reading that this could be
>helped by printing multiple time. Assuming the pigments don't get into the
>paper the texture would possibly improve as well.
>Thanks for your time and efforts
>----- Original Message -----
>From: "Judy Seigel" <>
>To: <>
>Sent: Thursday, November 17, 2005 11:48 PM
>Subject: 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.
> > > 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
> > > 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
> > >
> > >
Received on Fri Nov 18 10:14:03 2005

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