Re: Gum hardening -- top down?

Terry,

I understand I mist the point somewhat. I thought this down top hardening hypothesis was because some thought that the dichromate molecules gather at the surface of the paper and I tryed to disprove that.

In the much more probable case that dichromate molecules are distributed evenly in the emulsion, other laws apply but the end result would make the hypothesis that hardening start at the surface of the paper just as easy to disprove.

Assuming the emultion is only a bunch of various molecules distributed evenly in a thin coating on top of a piece of paper. The simple fact that they are present creates a physical barrier to light, UV or otherwise. Light considered as a particule, a photon, is so small that it could go in between those molecules and find a way to the papers surface but the probality that most of photons find there way to the paper surface is almost inexistant. The much more probable circonstance is that a large number of photon will be block by the top most molecules present in the emultion, what's left of the photons will be block by the next layer of molecules and so on. So an exponentially decreasing number of photons will make it's way to the paper if ANY. If you can't see the color of the paper through the emultion, there is an extremely low probability that a (UV) photon will make its way to the paper surface.

An analogy to this would go something like this. We fill a carboard box with styrofoam balls having several tooth pick poke into them to increase the area between the balls (the emulsion molecules) and use a shot gun shotting several 3mm pellets. (our photons). You'll agree with me that by doing this we should have more space between the balls then the ball occupy by themselves. I'm convinced it wouldn't take to many layer of such balls that we couldn't even see the bottom of the box and if we don't see it which mean infinitissimally small photon can't even get through and back to our eyes, there is not much chance a pellet will go through, even if it doesn't have to bounce back at us and pass again through the layers of balls. No shots required here...

Regards
Yves

  ----- Original Message -----
  From: TERRYAKING@aol.com
  To: alt-photo-process-L@usask.ca
  Sent: Wednesday, April 05, 2006 1:39 PM
  Subject: Re: Gum hardening -- top down?

  Yves

  What you, Sandy and I are all saying is that a dichromated image hardens at the top of the gum first.

  As Sandy has pointed out, and all of us who have made carbon prints know, that is why we need to transfer carbon prints.

  The top hardens first so leaving the layer closest to the surface unhardened. The layer closest to the paper/tissue is dissolved so that the hardened surface of the gelatine is transferred to another gelatinised sheet. One would not need to that if the the gelatine hardened at the paper first, As Yves points out that would be somewhat unlikely.

  Terry

  Terry

  In a message dated 5/4/06 6:19:20 pm, gauvreau-yves@sympatico.ca writes:

    Terry & all,

    the idea that a bunch of "free" molecules could aggreate in bundles or in layers without somekind of force acting on them goes against the laws of nature. If there was some (chemical) force attracting the dichomate molecules at the paper surface, which is not impossible per say, this would mean the paper could also attract other kinds of molecules and this would inevitably cause the paper to degrade at a much faster rate then what is currently observed. In other words the paper would be unsuitable for practically all types of process.

    Some may think gravity could cause the dichromate molecules to sink until they meat the paper and aggregate there but this is also impossible in this context. A good example of this is the air we all depend on, the concentration of molecules of air is for all practical purpose exactly the same anywhere in the room. Before you tell me that at the atmospheric level this isn't true which is exact I'll add that gravity is a very weak force and in a room it is basically annuled by the presence of heat (energy) which impart a significant mouvement to the molecules of air which make it quasily impossible that they will ever aggreate anywhere in the room. The same principles and physical laws apply for liquids and solids at different degrees of course.

    The only force that is significant enough to make the molecules gather on the surface of the paper would be chemical and as I already mentioned above the paper you all currently use have been design to be neutral chemically. In other words, by design, the paper you all used today don't have enough chemical potential energy to attract molecules at there surface or within them.

    I understand that adding chemicals, water, dichomate, gelatin, gum and what ever else will inevitably change the properties of the paper especially it's chemical neutrality. If this change in neutrality is significant enough that it causes some molecules to become "attractors" and force dichromate molecules to aggregate at its surface and bound with the paper molecules well I'm no chemist but I know that humidity and contaminants are always present in the air and the paper should be relatively immune to this kind of attack by design which make me believe that it should also be immune to dichromate as well. Is this actually a fact, I don't know but if it is possible that dichromate molecules compromise the papers chemical neutrality then I'm sure there are plenty of other chemical present out there to do just the same and the paper surface would become coated with them in a blink of an eye sort of speak. Our images wouldn't last very long and it would be a short time, just enough for a contaminant even of very low concentration to buildup to make it visible and bye bye image.

    Regards

    Yves

  Terry King FRPS

  RPS Historical Group (Chairman)

  www.hands-on-pictures.com/

  Moderated Discussion Group

  Post message: artaltphot@yahoogroups.co.uk

  Subscribe: artaltphot-subscribe@yahoogroups.co.uk
  Unsubscribe: artaltphot-unsubscribe@yahoogroups.co.uk

  1. An excellent thing is as rare as it is difficult.(Spinoza)
  2. A man's reach should be beyond his grasp or what's a heaven for.(Browning)
  3. Frustra fit per plura quod potest fieri per pauciora.(Occam's razor or 'Keep it simple!').
  4. Nullius in Verba (Horace), 'Take no man's word for it' (motto of the Royal Society).
  5. If ignorance is bliss, why are not more people happy ? (anon)
Received on Wed Apr 5 14:26:53 2006