FotoDave@aol.com
Sat, 27 Nov 1999 12:55:47 -0500 (EST)
In a message dated 11/26/99 11:06:22 PM Pacific Standard Time,
jseigel@panix.com writes:
> I've read from someone somewhere (Mike Someone-Ware?) speculation that the
> gum layer is much more unitary in its hardening, that the highlights are
> simply *less* hardened and soak away first.
Hi Judy, I don't know what "unitary" means in the above, but I agree that the
highlights soak away first. What happens is the hardened gum can still absorb
water and swell given enough soaking, so in the highlight area we have a
think layer of hardened gum, the water has to soak through this and reach the
unhardened layer, soften the unhardened layer and that got dissolved away.
On the shadow, we have a relatively thick layer of hardened gum, so it takes
a long time for the water to soak through this layer to reach the unhardened
part, so indeed the shadow section gets developed slower.
This slower rate of development with shadow gives a practical limit to
achieving Dmax with single-coat gum. In addition, since the thicker area
actually gets more filtering effect from the pigment, the shadow that needs
more exposure actually gets less exposure, so gum has a long shoulder if one
wants to include the deep deep Dmax (as Adam Kimball mentioned one time that
he got the visually linear range but then it took 5 or 6 steps further to get
the deepest black).
If one coat thicks, expose a lot (I mean, A LOT, like 30 minutes or an hour),
and soak long, one is able to get a long scale with gum (10 to 12 steps and I
have those steps), but that includes the loooong shoulder for the shadow (I
believe you called it "blocked up" shadows with little separation - the
separation is there but not useful enough for tone separation).
That's another reason why the SDC is different from standard gum. It is able
to achieve deep matte black but with full tone.
> (I would imagine
> that the "direct carbon processes" which pop up now and again (and
> lately!) use a thinner coat too.)
Well, I don't know how thin is thin, but yes I know the direct carbon process
that "popped up" recently uses a relatively thinner coat. ;)
Cheers,
Dave S
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