Re: (Gum) Tonal scale

Try Dichro on paper by itself and expose it with a standard test tablet and
see how it comes out...

In a message dated 12/6/05 9:25:55 PM, gauvreau-yves@sympatico.ca writes:

>
> Mark,
>
>  
>
> your are right about missing posts, something funny is happening with the
> server(s) I suppose.
>
>  
>
> At first I thought that in Joe experiments the stain could be caused by the
> dichromate "reacting" with the gelatine used in sizing but I tried the same
> test without sizing the paper. I though that whatever color I would see
> immediatly after the exposure would dissapear in the water but surprise, this dam
> dichro stain had a mind of its own and just stayed there on the paper. Now,
> I'm thinking there must be something in the paper that "reacts" with the
> dichro??? When I received Katharine message and went to see her own experiment
> made with gum and dichro I kind of said to myself what if there was only dichro
> on mylar or some other material that would most likely not "react" with the
> dichro??? So I tried a bit of dichro on glass and guess what??? If you think
> the dichro stayed on the glass, well it didn't. I also tried a couple more
> things like putting some dichro on paper, let it dry after and try to wash it
> off, yes it worked fine and as far as I can see I got a clean paper back. I
> even tried to force out the stains out of previously exposed dichro+paper using
> only water but contrary to unexposed dichro+paper I was left with what I call
> a 'ghost image' showing clearly the exposed area but without significant
> color, something like Katharine blue grey but definitively not paper white.
>
>  
>
> Why does it stay on some material and not on others??? I don't know for
> sure, I don't know either if it's a chemical or a physical "reaction" though I'm
> 100% sure there is a portion of what happen that is physical. I suspect the
> UV light causes a physical change in the structure of the dichromate, the
> details of which I'll leave to more knowledgable people. These changes must do
> at least 2 things at the same time if not more. One of these can be associated
> with the staining effect and the other can be associated with the conversion
> of soluble gum into clear insoluble gum. By the way, this
> 'insolubilisation'  can happen with many different materials.
>
>  
>
> From the experiment I did I would suspect some part of the dichromate
> (colored) byproduct after exposure must have some mean to stick on porous
> materials but it seems this stuff remain soluble in hot water and washes off
> relatively fast and the other near clear part either become insoluble and leave this
> 'ghost image' I saw or it as a stronger link with the paper that water alone
> can not break.
>
>  
>
> Regards
>
> Yves
>
>
Received on Tue Dec 6 20:41:59 2005