Re: Image formation in gum

On Dec 16, 2005, at 5:35 AM, Tom Sobota wrote:
>
> Anyway, I just uploaded a detail of the same image without scaling
> down so you can see the effect better. It is here:
> http://usuarios.arsystel.com/tksobota/Gum_on_glass_5.jpg

To my eyes, this shows even more clearly the pigment "stain" in the
form of excess pigment unevenly deposited across the glass, lighter in
some places and darker in others in an apparently non-image-related
way. It also shows how the hardened gum ends neatly at the edges of
the letters (you can see this especially on the T, U, and second F, you
can clearly see the hardened gum pulling off along the edge of the
letters. This is as one would expect, since the gum shouldn't have
hardened under the letters, which are black on the negative, and the
unhardened gum would have simply dissolved away from the letters
themselves, leaving clear glass, letters spelled out in negative space,
letters made of non-gum. The question of course is why the pigment
deposits itself so nicely on the non-image areas. I surely don't know
why that is, although I have a sort of theory, but in this case I think
this image shows pretty clearly that the gum is not involved.

I have prepared a page that shows that same effect in a different way,
but I just realized that I don't know how to do something in my new
version of GoLive, and I can't upload the page til I figure that out.
So it will be a bit longer. On my page, I show the tonal inversion in
images which are underexposed, so that it's abundantly clear that the
gum layer wasn't hardened completely.

>
> The same region, once dry (24 hs. in Madrid, which usually means
> _bone_ dry) is here:
> http://usuarios.arsystel.com/tksobota/Gum_on_glass_6.jpg
> This is not a photography but a monochrome scan by transparency.
> In this image the gum has dried so there are no 3D light effects as in
> the other images. There is indeed a difference in optical density
> between the letters.

And remember that if there is a reversal here, then it's a reversal of
a reversal, since the letters in black are a reversal in the first
place, as I said earlier.
Katharine
Received on Fri Dec 16 10:33:16 2005