Re: Why multiple exposure (was Re: (Gum) Tonal scale)

Loris,
i am so glad you said this, because I get 4-5 stops with gum (stops, not
steps, equating to 8-10 steps) not 6 or 7...but I do use ammonium dichromate
at 15% and not potassium dichromate.

I would encourage you to choose a time to expose at first before
calibrating--forget the steps--because when you are building your curve to
match that time, it'll take care of getting the gum to harden in the amount
of steps needed (that's a terrible way to explain it but you know what I
mean).

I chose 6 minutes UVBL for all layers. Then I found my curve for each
layer. Then I printed. This is the only process I did this with, as i have
calibrated cyanotype, VDB, palladium, salt, 6 BW papers, solarplate...all
those I chose my time based on, of course, the step tablet and my standard
printing time (SPT). But gum is different--it is a hardening of a layer,
not the same as the other processes at all. Well, maybe similar to
solarplate.

My SPT for gum is less than 6 minutes but this was not a stable enough
coating.

Why I chose 6 minutes--this was after many step wedges, tonal palettes,
etc--was it gave me a very stable coat that developed in an hour but that
could also be hastened on by a spray development without damage. So 6
minutes gives me options, where shorter times do not.

In choosing 6 minutes I did have to go back and redo my curves from the 5
minute time I had chosen before.

If my digitally challenged husband could say to me, "Wow, Chris, that's the
best print you've done yet" (of my "Squish" series--the cars), if he could
even NOTICE that it was the best one, it works for me!

I think gum is a combination of science and art--you need to "just do it"
but the tools at our disposal in this day and age are so wonderful we just
have to take advantage of them. It is an incredibly simple but incredibly
complex process.
Chris
PS anyone wanting to see a delicious Judy gum can go to p. 69 Photography's
Antiquarian Avant Garde by Lyle Rexer...

----- Original Message -----
From: "Loris Medici" <loris_medici@mynet.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, December 01, 2005 1:34 AM
Subject: RE: Why multiple exposure (was Re: (Gum) Tonal scale)

Hi Judy, I was making tests for tricolor gum. I'm trying to find the
right amnt. of pigment, gum and dichromate + strength of dichromate:

The pigment (tube) is Schmincke Cerulean blue tone (PW 4 + PB15:3) -
Yes, I know it contains zinc-oxide. I first poured the whole tube in a
film canister, then I added gum arabic (stirring, until the canister was
completely full) making a pigment stock solution. Later, I diluted this
stock solution 1:2 with gum arabic, then I added to this equal amnt. of
5% ammonium dichromate. I exposed it for 6 minutes. Developed face down
in still water (changing it every 10 minutes) for about 1 hour.

I got 16 clearly defined steps with the 31-step tablet. This makes 0.1 x
16 = log 1.6 negative density range. When you translate this into
21-step tablet (every steps are 0.15) it makes 1.6 / 0.15 ~= 11 steps.
And the max print density was slightly less than single coated classic
cyanotype (quite acceptable).

Does this makes me clever, experienced? ;) I don't think so, I guess it
makes me very very lucky. :)

BTW, what I trying to achieve is to standardize my pigment + gum +
dichromate emulsion mixes and exposure time for each color, so that they
all give me the same number of steps. Only after managing this I will
start to build curves and attempt to make tricolors. (Not that I feel an
urge to do tricolor gums - just for its fun...) What do you think about
this strategy?

Regards,
Loris.

-----Original Message-----
From: Judy Seigel [mailto:jseigel@panix.com]
Sent: 01 Aralık 2005 Perşembe 07:19
To: alt-photo-process-l@sask.usask.ca
Subject: Re: Why multiple exposure (was Re: (Gum) Tonal scale)

> I really got 8 STEPS not STOPS and I don't understand what
> could be the magic about that?

Because 6 or 7 steps is all an experienced gum printer would get in one
coat, but most likely in pale tones (which are much easier to get more
steps with because the darks don't block up). Getting them with enough
depth to be a full picture, without requiring several coats on top of
one
another to build up the tone, is, again, a sign of expertise.

And yes, I speak of steps.
Received on Thu Dec 1 09:21:35 2005