Re: (Gum) Tonal scale

Man, this is like playing darts blindfolded, or something of the sort.
Everyone is replying to a different set of posts, in a different order.
It's pretty crazy......

I didn't see Yves' post that Mark is responding to here, and have a
couple comments to it.:

If you "print" with plain dichromate, the dichromate will react with
the factory sizing in the paper, even if you don't add extra sizing,
and will form a crossliked matrix, even an image if you use a negative
with it. (I uploaded some examples of this some months ago and may
still have them around somewhere). If you're a person who gets
dichromate stain in your practice, this matrix will be stained so you
can see it; if you're not, the matrix will be invisible, unless you
hold it at an angle to the light, and then you'll be able to see it in
relief. (These things are also true of unpigmented dichromated gum.
Why some people get dichromate stain and others don't has occupied many
weeks of discussion on this list and hasn't been resolved, but I don't
think it makes any difference practically to the crosslinking process.

What I showed on mylar I also get on paper, with unpigmented gum. If I
print an image in unpigmented gum on paper, I get exactly the kind of
effect I keep telling you about, where you can't see the image until
you turn it to the light and then you see it in relief. ( It's really a
pretty cool effect. I've always wanted to do something with it for an
exhibition print, but haven't got around to it yet. ) If I have time
tomorrow, I'll show you. The problem is that I can't show the
invisible matrix because the scanner won't see it; I would need to take
it at an angle, and I don't own a digital camera to do that. But maybe
I can figure out a way.

Katharine

On Dec 6, 2005, at 6:41 PM, Ender100@aol.com wrote:

> 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 Wed Dec 7 01:20:09 2005