Re: Staining was Re: (Gum) Tonal scale

This one went astray so I'm sending it again:

Yves wrote:

>>>
>>> You basically said to me (and us) the other day that ounce all the
>>> gum as
>>> harden any further exposure would cause the remaining active
>>> dichromate to
>>> cause staining but there seem to be other reason(s) that could cause
>>> staining, if exposure alone was the cause of staining then we should
>>> see it
>>> in the highly exposed areas not in the barely exposed areas as is
>>> sometime
>>> the case with tests made with a step tablet. It as been called
>>> "inversion"
>>> on this list.
>>>
>
>
> Sorry, I didn't realize there was more below the questions. You're
> confusing dichromate stain here with pigment stain. I said that (in
> the particular case that you were asking about) the dichromate stain
> was caused by overexposure, but that there are many different possible
> causes for dichromate stain in other cases. But here, you're talking
> about pigment stain, which is an entirely different issue, and which
> is not IME related to exposure. I haven't been following that thread
> on tonal inversion and so I don't know what has transpired in that
> discussion.
> Katharine
>
>
>
>>>
>>>
>>> ----- Original Message -----
>>> From: "Katharine Thayer" <kthayer@pacifier.com>
>>> To: <alt-photo-process-l@sask.usask.ca>
>>> Sent: Thursday, December 08, 2005 12:42 PM
>>> Subject: Re: (Gum) Tonal scale
>>>
>>>
>>> Okay, I edited the gum colors page to remove the irrelevant elements
>>> that distracted some of you before, so you can see that for purposes
>>> of
>>> this discussion, the page isn't about stain and attempts to remove
>>> it,
>>> but is intended to show a comparison of the colors of unpigmented
>>> crosslinked gum, stained crosslinked gum, and stained crosslinked gum
>>> from which the stain has been removed with a clearing agent.
>>>
>>> http://www.pacifier.com/~kthayer/html/gumcolors.html
>>>
>>> I've always intended to go back and finish this page, adding the
>>> colors of stained gum when it is scraped off its support wet (deep
>>> green) and dry (ground-coffee brown) I don't know what those colors
>>> mean in terms of the chemistry of the process, or how (or whether)
>>> they
>>> relate to gum practice, but I just think it's interesting, the
>>> different colors that unpigmented gum will take under different
>>> conditions. These were some of the things I discovered about gum
>>> when I
>>> was working to produce gum for analysis.
>>> kt
>>>
>>> On Dec 7, 2005, at 11:27 AM, Katharine Thayer wrote:
>>>
>>>> Okay, I've spent some time this morning trying to show you how for
>>>> me,
>>>> a crosslinked matrix of unpigmented gum is clear and colorless, not
>>>> just on mylar but also on paper (here, Arches bright white).
>>>>
>>>> First, I printed two step tablets side by side, which I show you
>>>> here.
>>>>
>>>> http://www.pacifier.com/~kthayer/html/gumnocolor.html
>>>>
>>>> All you see is a white field. If I still had my old version of
>>>> GoLive,
>>>> I could have given the page a different-colored background so you
>>>> could at least see the paper against the background, but I don't see
>>>> where to do that in the new version; it's not where it used to be.
>>>> As
>>>> it is, the white of the paper is close enough to the white of the
>>>> background that it doesn't distinguish on the page.
>>>>
>>>> Then I tried to figure a way to make the gum image (this is why I'm
>>>> not sure I can agree to reserve the term "gum image" for a gum image
>>>> with pigment in it) visible so you could be convinced it was
>>>> actually
>>>> there. I thought of doing a dusting-on process, but I don't have
>>>> any
>>>> dry pigment, so I tried powdered graphite, and what a mess. I'm
>>>> obviously not quite up on how to do the dustin-on thing. Anyway I
>>>> ended up with black powder all over the studio; I ruined my little
>>>> puff bottle that I use to puff a little powder onto the back of FP4
>>>> to
>>>> keep it from making Newton's rings against the glass when I print
>>>> with
>>>> FP4; I put the graphite into it in a vain attempt to get finer
>>>> clumps
>>>> of graphite, and now I will have to buy a new one to powder FP4
>>>> with,
>>>> and after all that, all I had was a big mess. So I'm giving this up
>>>> as a lost cause; I'm cross and I'm done with this for now. You'll
>>>> just
>>>> have to take my word for it, I guess.
>>>> Katharine
>>>>
>>>>
>>>>
>>>>
>>>> On Dec 6, 2005, at 11:18 PM, Katharine Thayer wrote:
>>>>
>>>>> 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 Thu Dec 8 21:16:06 2005