Re: Gum hardening: top down experiment

Hi all,

I think in all this discussion about the top down hardening or vice-versa
many of you forget one, if not the most important, point. Unless physical
laws have change recently behind my back, Ok not behind my back I just
haven't look at it lately but anyway before anything happen with the
chemical stuff, be it the gum, the pigment, the dichro and even the paper,
the photons (light) must reach these molecules which ever they are and the
laws of physics say that if a photo hits an atom in one of those molecules
it will be absorb, the mechanism of which is irrelevant at this time.
However thin you can make a gum emultion on a piece of paper or whatever,
this emultion will deposit on the substrate an extremely large number of
molecules and as all of you know already these molecules are made of atoms.

The point is this, when a photon comes in to meet with this emulsion it will
either strike an atom on its path through all these molecules or it will go
through, it could even go through the substrate if it's not completely
opaque (obviously). This is definitely top-down or to be more accurate
photon always hit atom from the side they come from or if you prefer
"hardening always happens in the same direction as the path of the photons".

Now, why in the world would someone be led to believe that it could be the
other way around? The most probable reason I can think of goes about like
this, our photon when they hit an atom can cause the atom to emit another
photon (with distincly different properties) which in effect may look like
the photons are bouncing of atoms. If the conditions are right, most
probably when the emultion is relatively less opaque then the substrate
which mean that a larger number of photons will go through without striking
an atom then the number of photons that will be blocked. If the ratio is
such that the photons emitted from the substrate, it is possible, having
different properties, that they hit a sufficient number of atoms from the
back that it appears that the emultion hardens from the back. All I'll add
here, if you think of it, the hardening always follow the path of the light
even in this case.

But is it possible to observe and measure a larger density of hardened gum
near the substrate side then on surface of the emultion? Most probably not
and here is why. This as to do mainly with the law of conservation of energy
and the fact that UV light as a higher energy level then visible light but
here are other facts that may be useful.

Fact 1: If you look at the spectrum of the light you use, you will most
likely see in the UV wavelength range some decrease (vertical) as the number
gets lower (horizontal).
Fact 2: It is not possible for a photon having a wavelength of say 400 nm
to cause an atom to emit a photon with a lower wavelength then 400nm.
Fact 3: The lower the wavelength the higher the frequency and the higher
the energy level and vice-versa.
Fact 4: Not all photons will cause an atom to emit another photon.

Combining all these facts together we know now that only UVC photons can
cause atoms to emit UVA or UVB (also UVB => UVA)(fact 2), knowing that most
of our light source present much lower level of UVC then UVA, UVB and all
other and longer wavelengths of light and knowing (fact 4) only part of the
atom will emit a photon just in case it wasn't already enough. There is a
very low probability if any that enough UVC and UVB photons will go through
the emultion, hit an atom in the substrate and be emitted as UVB or UVA such
that they could hit an atom in the emultion and cause sufficient hardening
from the back to outweight the combine effect of all UVs coming directly
from the source. Adding to that, if say 95% of all light goes through the
emultion in one direction it is obvious that the same relative number will
come back in the other direction without hitting any atoms. In other word,
light comes in from the surface, some of it will be lost as it goes deeper
in the emultion, at the substrate we'll loose some more, some through the
substrate itself, some will be absorb there and some will bounce of atom and
never come back to be useful and of what little is left and coming
backwards, the same relative amount (%) that got through in the first
direction will be lost again.

In conclusion, while I tried to keep an open mind to the possibility it
could be possible, after all this, well, there is simply no way, no physical
way, no logical way that hardening could happen bottom up. All the
observations made so far (mostly by you all) are explained away and if you
are still not sure they are, I'll be glad to put my weight on the balance,
in the physical sence of course (200 pounds+)

Regards
Yves

----- Original Message -----
From: "Sandy King" <sanking@clemson.edu>
To: <alt-photo-process-l@usask.ca>
Sent: Wednesday, April 12, 2006 11:21 PM
Subject: RE: Gum hardening: top down experiment

> >
> >Which is to say, I would say a print on plastic is a different
> >medium, an OHP-o-Graph, perhaps. If it proves to be hardened from
> >top or bottom, very interesting, but I print on paper, and much of
> >what I've read (including the sainted, notorious, blessed/evil Mike
> >Ware) AND my own experience shows the paper to be an active part of
> >the process.
> >
> >The dichromate (with or without gum) DOES sink into the fibers of
> >the paper. But does it just lie there like a lotke (it's Passover,
> >folks, if I could spell lotke confidently I'd tell you more), or is
> >it part of the action? My impression is that it's active, and I
> >point out that IME each paper performs differently. I suspect more
> >than just sizes are different, but the fact that different papers
> >need different sizes is also a clue.
> >
> >J.
>
>
> I don't disagree with any of this. A print made on plastic exposing
> through the surface of the plastic would have IMHO different image
> characteristics. In fact, I have stated that opinion several times.
>
> As for gum on paper, I have no opinion, other than until someone
> presents a compelling theory as to why image formation is not
> primarily top down I will continue to believe that it is. Hopefully
> Chris will address that in her class this summer in SF.
>
> Sandy
>
>
Received on Thu Apr 13 05:51:18 2006