U of S | Mailing List Archive | alt-photo-process-l | Re: How many gum layers (Re: ferri sesquichlorati)

Re: How many gum layers (Re: ferri sesquichlorati)

Halvor, I've not seen either of these approaches, but neither of them makes much sense to me.

I assume here we're talking about printing a negative that exceeds the short tonal range that gum is capable of in one printing.

The usual recommendation is multiple printings using more pigment and less exposure for the shadows, and less pigment and more exposure for the highlights. This works well for me. (I don't think it matters what order you do it in. I like to lay in the highlights and midtones first, with a less-pigmented emulsion and a longish exposure, and then put in the shadows with more pigment and less exposure. But I can imagine someone wanting to put in the darks first (easier registration, for one thing) and the lights second; I don't think it makes any difference.)

Then there's a school of thought that says you should make a contact negative that brings the tonal scale of the original negative down to the short range of gum, but that's never made sense to me because you lose so much of the subtlety when you do that; I prefer to print all the tones in the original negative. So far, the only way I've ever seen to get subtle tonal gradation throughout a long tonal scale (with the one exception of Marek's back-printed flowers) is multiple printing, as described above.

On Oct 24, 2006, at 2:05 AM, Halvor Bjørngård wrote:

Katharine, thanks for input .. are still "absorbing" this ...

One last (maybe) gum question..

I have seen two approaches for building up the tone scale.. One is to use a
constant pigment concentration and on subsequent layers reduce the exposure

The other to use a constant exposure time but to increase pigment
concentration for each layer (which with my test reduces sensitivity

Is one method more usual than the other, I originally only knew the first
one.., Is one method best, or is this just a matter of purpose ... Comments
any one ?

On 10/24/06 12:02 AM, "Katharine Thayer" <kthayer@pacifier.com> wrote:

Halvor, I'm coming late here; you've just posted your revisiion, but
since I've already written this I'll go ahead and send it:

  I agree that how many layers depends  on the thickness of the
layers (BTW the same gum emulsion goes on thicker on nonabsorbent
surfaces than paper IME) and on the substrate (my experience has been
that I can print fewer layers on nonabsorbent substrates rather than
more, but that may also be partly related to my experience  that the
layers are thicker on the nonabsorbent substrate).

As to the relief effect Keith described,  I think it's also related
to the paper you use how many layers it takes to get this effect.
With Arches bright white,  if I'm printing a fairly high-contrast
image (very thick areas of gum interspersed with very thin areas of
gum) I get this effect even with one layer of gum. If you look at the
print from the back, you see the image in relief in the paper, that's
how pronounced the relief effect is.  I thought at first it was a
differential shrinking of the paper around the gum and assumed I
could avoid the effect by preshrinking the paper, which I don't
ordinarily do, but found to my surprise that preshrunk paper does the
same thing; it's apparently a relief thing not a shrinking thing
that's going on.

By the way,  a couple of years ago I took one of these warped prints
and had it dry-mounted to flatten it, and announced that solution
here, but I don't think I'd do that to a finished print again,
because it seems like it would mash down the relief.  People seem to
be fine about the relief effect, in fact they like it, so I've
decided not to worry about it.  Like I said, it's only noticeable
with a print that's fairly high contrast.