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

On Thu, 1 Dec 2005, Loris Medici wrote:

> 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. :)

Actually Loris, as far as I'm concerned it makes you a wizard... I think.
I've never used cerulean blue for gum printing, let alone for tricolor. In
the versions I've used it simply had no covering power. Tho they did NOT
have white in them (as I recall) so were clearly something else. Still, I
think 11 defined steps is very unusual, to put it mildly ... (at least in
my experience). In fact wouldn't 11 clearly defined steps be good for
VDB???

However, I would suggest (although weakly) that before you invest a LOT
more energy in the cerulean you test to see how nicely it plays with
others... I don't visualize it, but -- I wouldn't have expected 11 steps
either !

meanwhile, congratulations...

> 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?

   I think probably we're now into *personality* more than strategy. It
would NEVER be in my personality to try to standardize exposure time,
steps, et al -- and I doubt my materials and workroom would stand for it.
But it's clearly you -- so go for it !

Judy
Received on Fri Dec 2 00:53:20 2005