RE: Gum hardening: top down experiment

Yes, I should have said that saving the print by shortening the development
will work in many cases for actual gum prints. In the original
discussion/testing, however, saving the print might make interpretation of
the result difficult.

The set exposure time for our test would be the minimum time required to
make reasonable gradation when exposure is made from the back. For example,
one could expose so that 4 steps are obtained. Then use the same exposure
time for exposing from the front with the step tablet covered with a piece
of mylar. The idea is that we shouldn't underexpose such that both cases
will not work or overexposed so that both will work.

Dave
 

-----Original Message-----
From: Sandy King [mailto:sanking@clemson.edu]
Sent: Tuesday, April 11, 2006 3:40 PM
To: alt-photo-process-l@usask.ca
Subject: RE: Gum hardening: top down experiment

Dave,

And it works exactly that way in Carbon. If the exposure is too short we can
"try" to save the print by developing for a shorter period of time, then
"set" the gelatin in very cold water. If exposure is too short we develop
for a longer period of time, and/or increase the temperature of the water.

For testing I would settle on a set exposure time. The problem here, none of
the other parameters are fixed so what exposure time should you try?

Sandy

>Oh, in that case yes, it must be underexposure then. I think you need
>an exposure that can take at least full development (or nearly full
>because it is hard to define what is full). If exposure is too short
>but we "save" it but developing short, then it is hard to make
>judgement on what we are trying to test for this case. Saving the print
>might work for actual prints, of course.
>
>Dave S
>
>
>-----Original Message-----
>From: Marek Matusz [mailto:marekmatusz@hotmail.com]
>Sent: Tuesday, April 11, 2006 1:48 PM
>To: alt-photo-process-l@usask.ca
>Subject: RE: Gum hardening: top down experiment
>
>Sandy,
>The piece did not fade as such, the esposed gum layer was so soft it
>started running down the transparency once I hanged it to dry. Actually
>it developed so fast, I pulled it out from the water too late. Somebody
>else was right here, you really can not arrest gum development as it is
>soluble in cold water as well.
>I will try more exposure.
>Marek, Houston
>
>>From: Dave Soemarko <fotodave@dsoemarko.us>
>>Reply-To: alt-photo-process-l@usask.ca
>>To: alt-photo-process-l@usask.ca
>>Subject: RE: Gum hardening: top down experiment
>>Date: Tue, 11 Apr 2006 12:56:23 -0400
>>
>>Perhaps "a piece of ice" might not be a good analogy. A piece of
>>dampened spongue might be closer.
>>
>>Dave
>>
>>-----Original Message-----
>>From: Dave Soemarko [mailto:fotodave@dsoemarko.us]
>>Sent: Tuesday, April 11, 2006 12:30 PM
>>To: alt-photo-process-l@usask.ca
>>Subject: RE: Gum hardening: top down experiment
>>
>>It might be because the development is not complete, so there is still
>>a lot of unhardened gum (which contains water). Well, actually even
>>the hardened gum is soaked up with water at that point, so the water
>>will continue to develop the surrounding gum. Sort of like if you put
>>a piece of ice on jello versus you put a piece of ice on gum. The
>>first case will have no problem whereas the second will make a mess.
>>
>>
>>Dave
>>
>>
>>-----Original Message-----
>>From: Sandy King [mailto:sanking@CLEMSON.EDU]
>>Sent: Tuesday, April 11, 2006 12:19 PM
>>To: alt-photo-process-l@usask.ca
>>Subject: RE: Gum hardening: top down experiment
>>
>>
>>Dave,
>>
>>You make some good points.
>>
>>Just a couple of follow-up comments.
>>
>>I know that gum will continue to develop in cold water, but my
>>understanding was that Marek's print was removed from the water and
>>hung up to dry. If that is so, I am still confused as to why it would
>>fade.
>>
>>Sandy
>>
>>
>>
>>
>>
>> >Hi Katharine, Marek, Sandy, Judy, and whoever interested, >
>> >Thanks for your efforts and sharings on your findings.
>> >
>> >About the tests, however, I have a few suggestions:
>> >
>> >Katharine, you probably shouldn't expose longer than usual and
>> expose >the front and back differently because that will affect
interpretation.
>> >Let's try to step back and look at our hypothesis first. Let's say
>> we >assume that hardening is from top to bottom (we don't have to
>> agree >on this, but we can take any view and start from there). The
>> test >then, is to expose it not too much from both side. If
>> hardening is >from top to bottom, the one exposed from the front
>> will not reached >the base, so it has nothing to hold on, so it will
>> flake off, whereas >the one exposed from the back will grab the
>> base, so it will have
> > >some image. But if expose a lot (or strongly), then probably both
>> >will have an image because even the one exposed from the front will
>> >be exposed sufficiently to reach the base. Now the contrast of the
>> >two might be different, and so we might start to make different
> > >inference from there,
>>but that is not the original goal of the test.
>> >
>> >Suppose that we expose it normally, and get a fine image for the
>>one
>> >exposed from the back but not for the one exposed from the front,
>>we
>> >pretty much proved our hypothesis. But suppose we don't get an
>>image
>> >from either one, then we need to adjust. It might be that the mylar
>> >might be cutting off a lot of UV, so we need to expose more. But if
>> >we expose more, is it a fair comparison because the front one
>>doesn't
>> >have
>>the
>>UV blocking by the mylar?
>> >So in order to have a reasonable test, we need to increase expose
>>but
>> >also cover the front side by a piece of mylar during exposure.
>> >
>> >Our tests seem to be something in between. The fact that the image
>> >continue to dissolve after development seems to suggest that
>>exposure
>> >is not enough so there is still a lot of unhardened gum (Sandy, to
>> >answer the question of why this is happening in gum but not in
>> >carbon, the difference in mechanism is that gelatine doesn't
>>dissolve
>> >in cold
>>water
>>whereas gum does).
>> >
>> >My suggestion would be to expose perhaps a step tablet with double
>> >the amount of time used for exposing through the back, but when
>> >exposing the front, cover it with a piece of mylar.
>> >
>> >And thank you again for all your efforts. I am by no means asking
>>you
>> >to
>>do
>> >a certain test. It is simply a suggestion from me, a lurker now. :-)
>> >
>> >
>> >Dave
>> >
>> >-----Original Message-----
>> >From: Katharine Thayer [mailto:kthayer@pacifier.com]
>> >Sent: Tuesday, April 11, 2006 11:22 AM
>> >To: alt-photo-process-l@usask.ca
>> >Subject: Re: Gum hardening: top down experiment
>> >
>> >Marek, thanks for your response. My patience for this discussion
>>was
>> >coming to an end just as your post popped into my mailbox; you have
>> >revived me. A couple of comments embedded below:
>> >
>> >
>> >On Apr 11, 2006, at 7:41 AM, Marek Matusz wrote:
>> >
>> >> Katharine,
>> >> I was very impressed with your results and thanks for
>>contributing
>> >> to this discussion in a positive and constructive way. Looking
>>at
>> >> your scans I would conclude that heavily pigmented gum layers on
>> >> unabsorbant substrate do harden from the top down, just like
>>other
>> >> dichromated colloids.
>> >> I see very nice tonal gradations in the print exposed from the
bottom.
>> >> The three variables (gum, dichromate and pigment ratios) are not
>> >> optimised, but at this point I am looking for illustration of
>> >> principles, rather then perfect prints.
>> >
>> >Thanks, I agree.
>> >
>> >> I did a similar experiment last night. I coated a heavily
>> >> pigmented and thick layer of gum on a transparency material that
>>I
>> >> use to print diginegatives (HP brand). This brand has a nice
>>sandy
>> >> feel to it, so I though it would help to hold the gum. I exposed
>> >> coated pieces for
>> > > twice my usual times, one through top, the other from the bottom.
>> >
>> >For whatever it's worth, I exposed the front-exposed print on mylar
>> >for
>> >6 minutes, which is 4X my usual time for that negative, and the
>> >back-exposed print for twice the time of the front-exposed one (12
>>minutes).
>> >
>> >> The piece exposed from the top flaked off rather quickly leaving
>> >> no image. The was no image that I could see at any point. The
>>piece
>> >> exposed thorough the bottom once in the water started behaving
>>like
>> >> a carbon print, where the colloid was dissolving in water, rather
>> >> then flaking off. After about 3 minutes I was excited to see a
>>full
>> >> tonality image, with beautiful tonal gradations. Unfortunately
>>the
>> >> image continued to develop even afet I took it out of water and
>> >> hanged it to dry.
>> >
>> >This is exactly what happened with the front-exposed print in my
>> >experiment; it looked okay, although very high-contrast, when I
>>took
> > >it out of the water, but by the time it was dry the hardened gum
> had
>> >melted and puddled on the mylar. (This is not what usually happens
>> >when I print on scuffed mylar using a more normal emulsion).
>> >
>> >
>> >
>> >> This morning there was only a faint image left on the piece of
> > >> transparency. I will give it another try with much longer
> exposure
>> >> and perhaps lower dichromate to get more depth of UV penetration
>> >> and hardening and higher Dmax.
>> >>
>> >
>> >I look forward to your report,
>> >Katharine
>> >
>> >
>> >
>> >>> From: Katharine Thayer <kthayer@pacifier.com>
>> >>> Reply-To: alt-photo-process-l@usask.ca
>> >>> To: alt photo <alt-photo-process-l@sask.usask.ca>
>> >>> Subject: Gum hardening: top down?
>> >>> Date: Mon, 10 Apr 2006 11:33:03 -0700
>> >>>
>> >>> Okay, I've coated a very thick, very heavily-pigmented gum
>> >>> emulsion on mylar and printed it from the front and from the back.
>> >>> A couple of comments before I give you the URL:
>> >>>
>> >>> (1) though the emulsion was very heavily pigmented, two things
>> >>> resulted in not a very deep DMax: (a) the fact that I used ivory
>> >>> black, a transparent pigment (if I were to do it again, I'd use
>> >>> lamp
>> >>> black) and (b) the fact that it's printed on a transparent
>> >>> material and was scanned as a transparency, with the light
>> >>> shining
>>through it.
>> >>> But the thing to note is, be that as it may, the DMax is about
>> >>> the same in both prints.
>> >>>
>> >>> (2) there's a light brown pigment stain (ivory black is a
>> >>> brownish
>> >>> black) in both prints that is probably a function of the heavy
>> >>> pigmentation. It hardly shows in the prints themselves, but for
>> >>> some reason was accentuated in the scanning.
>> >>>
>> >>> (3) I don't honestly know what to make of the results. If you
>> >>> look just at the prints on mylar, you'd have to conclude that
>> >>> back- printing is much superior to front-printing, at least for
>>a
>> >>> thick coat on mylar. But if you compare the back-printed print
>>on
>> >>> mylar to the regular front-printed gum print (using a less
>> >>> heavily-pigmented emulsion) on paper (at the bottom of the
>>page),
>> >>> it's hard to claim that the back-printed print is superior. But
>> >>> since they are on different materials, it's apples and oranges.
>> >>>
>> >>> So I guess if I were forced to draw a conclusion from this
>>rather
>> >>> inconclusive test, I'd say that if you are going to print on
>> >>> mylar using a very thick and heavily pigmented emulsion, then
>> >>> you'll probably do better printing from the back. But if you're
>> >>> printing on paper, you can get fine results printing from the
>> >>> front with a less pigmented emulsion.
>> >>>
>> >>> http://www.pacifier.com/~kthayer/html/topdown.html
>> >>>
>> >>> Katharine
>> >>>
>> >>>
>> >>
>> >>
>> >>
>>
>>
>>
>>
>>
>>
>>
Received on Wed Apr 12 00:20:08 2006