From: ericawd (ericawd@mem.quik.com)
Date: 02/24/03-09:03:19 AM Z
Lurker, Candace Spearman, gum printing in Memphis, TN
----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@skyway.usask.ca>
Sent: Sunday, February 23, 2003 12:44 PM
Subject: Re: gum printing
> Christina Z. Anderson wrote:
> >
> >
> > Gum questions:
> > 1. Which colors absolutely do not work? I have these notes: hooker's
> > green (washes out), emerald green, and any chromium based colors.
>
> I've been told by someone I generally find reliable that the truism that
> chromium based colors don't work with gum isn't actually true. I haven't
> tested this assertion myself but just pass it on for whatever it's
> worth, and maybe someone else has better information on this. The person
> who told me this is unfortunately not a member of the list so can't
> speak for himself on the matter.
>
> I'm sure I've used hooker's green without a problem, but have never used
> emerald green. Of the many colors I've used, I've never found one I'd
> say doesn't work. The thing is that each pigment has its own
> characteristics and you have to learn the proportion of gum to pigment
> and the exposure that gives the desired results for each individual
> pigment, but I haven't seen a color that can't be brought to heel. I
> know of someone who uses the Daniel Smith moonglow very successfully,
> for example.
>
> > 2. Do you use am di or pot di? I learned on am di and am wondering if
it
> > is worth it to buy some pot di. Webb/Reed say only use am di if you
can't
> > get pot di. Hirsch says use am di. Go figure. I just want to know
what
> > you guys use, and I do have the notes from the past about am di being
lower
> > contrast/muddier but then those saying that isn't the case. Does it
boil
> > down to what you are used to?
>
> After a lot of observation and discussion, I've become convinced that
> how well ammonium dichromate works is a function of the intensity (and
> possibly the heat production) of the light used. Some people using very
> strong lights (including the sun) may find that the ammonium dichromate
> is too fast for their lights and will result in overexposure and
> dichromate "staining" which can change the appearance of the colors and
> result in a "muddy" appearance which isn't seen with cooler lights. So
> the answer is, it depends. In my practice, ammonium dichromate gives
> clear colors and no excess dichromate deposits, but as we always say,
> your mileage may vary. It's true that potassium dichromate gives more
> contrast (fewer steps) all other things being equal; whether you like
> that or not will depend on personal preference, although to some extent
> the contrast can be adjusted by changing the pigment/gum proportions. In
> my tests, ammonium dichromate can be printed with the same sharper
> contrast as potassium dichromate by using more pigment in the ammonium
> dichromate mix than is in the potassium dichromate mix.
>
> > 2a. If you diluted am di to the same percent as pot di would it be
> > equivalent in speed?
>
> Not precisely. To reduce ammonium dichromate to the same speed as
> potassium, you have to dilute it more than to the same percentage
> solution as the potassium. Assuming that a saturated solution of
> potassium dichromate is about 13% by weight, a solution of ammonium
> dichromate would have to be mixed at about 10% by weight, if my
> calculations are correct. There's a chart somewhere, maybe in Kosar,
> that gives these percentages. It's between 70 to 85%; that is, the
> percentage by weight of the ammonium dichromate should be somewhere
> between 70 to 85% of the percentage by weight of the potassium
> dichromate to get the same speed. I hope that's not too convoluted to
> make sense.
>
> > 3. What clearing agent do you use? I have come across sodium sulfite,
> > sodium bisulfite/metabisulfite, potassium bisulfite, and sulfuric acid
1%
> > solution. Does sodium sulfite truly do the trick so I don't have to
choke?
> > the metabi literally gives me instant asthma.
>
> I've always used sodium bisulphite but I do it outdoors because the
> fumes, as you say, are really noxious. I'll be interested in hearing
> other's experiences on the alternative agents. It's my opinion that
> sulfuric acid is necessary only for seriously overexposed prints which
> contain a lot of excess reduced chromium products, and shouldn't be
> necessary for a properly exposed print. And I disagree respectfully with
> those who say that prints with ammonium dichromate require more
> clearing; as I explained above I believe that's only true for those
> using certain kinds of lights.
>
> > 4. Has anyone used lemon juice in the sensitizer to insolubilize it,
> > decreasing exposure and giving better midtones? (Demachy,
Photo-Aquatint,
> > p. 39).
>
> Not me.
>
>
> > 6. How many gummists are there? I know Judy, Dave, Katherine, Joe, but
who
> > else isn't speaking up? Even part-timers?
>
> You mean on the list? I see Julian Smart and Hamish Stewart have already
> spoken up. Sarah Van Keuren used to be here but I think she isn't now.
> Ernestine Ruben watches the list but doesn't speak up as much as I'd
> like, and I hope she won't mind my mentioning her name. Suzanne Izzo is,
> or was, here, ditto Mary Pat McNally and Harry Bonham. Dick Sullivan is
> a gum printer from way back. And there's the group of guys who started
> by printing gum over platinum, some of whom are now printing gum by
> itself. Kerik Kouklis, Clay Harmon, and others. That's just a few of
> the gum printers I'm aware of that hang out here, besides the ones you
> already mentioned, and it would be great to have more of the lurkers
> pipe up.
>
>
> Your class sounds great, and I hope you'll keep us posted on how it
> works.
> Katharine
>
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