Re: Image formation in gum

I'm also glad that you found this new example, since that is what I see in
my test: soot, as you say, but soot imbedded in a very thin matrix of hardened
gum. It can be removed rubbing with something but without having to scrape
it with a knife. But, mind you, this layer is very thin and cannot be seen with
the naked eye. Even with a binocular loupe this layer is difficult to separate
visually from the glass.

Yesterday I was somewhat surprised with your observation that the image was
just carbon black sitting on the glass. That implied all the gum
dissolving around
the pigment particles without carrying it along? A layer of particles
of pigment
sedimented on the glass and attracted to it electrostatically?
Possible, but not in
my case.

But I agree with you that it _is_ a great looking image. Even if as
it is it's not too
strongly adherent, perhaps you could attempt to fix it with some fixing spray,
egg white, or a coat of gelatin, no?

Tom Sobota
Madrid, Spain

At 19:25 17/12/2005, you wrote:

>On Dec 16, 2005, at 1:59 PM, Katharine Thayer wrote:
>>
>> But I also think it's not just an either-or thing, it's probably
>> a continuum, so there are probably intermediary steps where there
>> is some gum involved. I don't know, I'm just guessing.
>
>I'm glad I said this last, because I've just encountered an example
>of something that probably fits this in-between category. It's lamp
>black on glass, where some of the hardened gum came off. It doesn't
>represent a tonal inversion kind of deal; the letters didn't print
>in black, for example. there is a definite pigment stain left
>behind where the hardened pigment floated off, but in this case, the
>pigment tone is very definitely not removable. If you look closely
>you can see a couple of places where I scratched it with a
>fingernail, but it's definitely not easily wipable like the pigment
>I was wiping off yesterday where there was a definite tonal
>inversion effect. (One possible confound is that this is on etched
>glass while the ones I did yesterday were on plain window
>glass). But at any rate, I think this is probably an example
>showing that this phenomenon is a continuum, but whether or how the
>gum is or is not involved in this case, I'm at a loss to guess. It
>seems to me that there isnt any gum there, but then why? as Tom said
>yesterday about something else. I think this is fascinating, but
>difficult to fully explain in all its possible variations.
>Katharine
Received on Sat Dec 17 14:35:42 2005