Re: Staining was Re: (Gum) Tonal scale

On Dec 8, 2005, at 10:55 AM, Yves Gauvreau wrote:

> Katharine et all,
>
> On the page you refer us to below, you say for exemple #2 "Gum
> deliberately
> exposed in the sun til stained with dichromate stain" and I would like
> to
> know what is the actual cause of the stain???

Yves,
when I want to deliberately create dichromate stain, as I did in that
case, I do it in the sun because it takes too long for me to create
dichromate stain exposing with my photoflood.

The stain is a function of exposure time in the sun, not of the sun
itself, because I can print gum in the sun without dichromate stain,
simply by limiting the exposure to a few seconds, and in fact when I
want to make a lot of prints fast, and if the sun is shining, that's
how I do it. 5 or 10 seconds, depending on the strength of the sun,
makes a perfect print with no stain.

There are many different causes, however, that can account for
dichromate stain, not just overexposure. As I said earlier in this
thread, the list has occupied itself sometimes for weeks trying to
understand what causes it and why some people get it and others don't.
If you're interested in all the things that have been suggested as
causes for dichromate stain, I would look for those discussions and
read through them. It's yet another one of those many unresolved
issues that abound in gum.
Katharine

>
> Is it the exposure time???
>
> Is it the gum???
>
> Is it the sun light???
>
> Is it the heat???
>
> Is it a combination of these???
>
> Is it something else???
>
> 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.
>
> If anyone as reference on this staining thing I'd be interested to
> learn
> more about it.
>
> Regards
> Yves
>
>
>
>
> ----- 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 17:17:54 2005