Re: Gelatine is also '' a '' gum but not Gum.

On Tue, 4 Apr 2006, Sandy King wrote:
> In general, although there are some important working differences, they all
> work on the same basic principle, ie. exposure (and hardening of the gelatin)
> is from top to bottom, with no transfer of the image (as in carbon and
> carbro).

Actually, the distinction generally given in "the literature" is that
because carbon hardens from the top down, transfer is necessary (although
"direct carbon" without transfer has its own litany), while gum (as far as
has been established to date) hardens at the surface of the paper.

Among proofs of that I could cite, I mention only that, depending on mix
and exposure, it's often possible to wipe off the TOP of a gum layer,
while the bottom, the part in/on the paper holds.

Paul Anderson devised a theory that gum latched onto paper texture, and
illustrated it with a diagram showing the dear little gum molecules
hanging on for dear life. This has been cut and pasted into manuals from
that day to this, but, evidence suggests, although it may happen in
whatever cases and conditions, it doesn't have to.

J.
Received on Tue Apr 4 17:52:00 2006