[alt-photo] Re: IDEA? NEW ALT PHOTO BOOK

[Peter Friedrichsen]

I do agree with Katharine that the fibers do act as an anchor, but 
the fibers must still be attracted to the gum emulsion (hydrophilic). 
For instance, a very thin layer of a hydrophobic coating, i.e. a 
paraffin, or silicone oil applied to the paper will not allow the gum 
emulsion to adhere even if that coating is applied in very small 
amounts, so if the PVA is more hydrophobic than the hardened gelatin 
then it stands to reason that the adhesion may be poorer.

Peter Friedrichsen



At 02:08 PM 04/23/2010, you wrote:
>Whatever size is used,  the gum attaches to the paper fibers rather
>than to the size, so the material used in the size shouldn't make any
>difference to how the gum adheres to the paper.   Difficulties with
>size arise when the size becomes so thick or heavy that it clogs the
>surface fibers and leaves nothing for the gum to hang onto; then the
>hardened gum tends to slide off into the water.  This is true
>whatever size is used, and this is why the optimal dilution of PVA
>size is different for different papers, because different papers have
>different surface qualities, and the size needs to be diluted enough
>that it soaks into the paper leaving surface fibers ("tooth") open
>for the gum to attach to.  So no, the gum doesn't "sit" on top of PVA
>size any more than it does on top of a gelatin size.
>
>Paul: Since the unreacted dichromate and soluble gum wash off in
>development, there are no reaction products left in the finished and
>dried print, so there would be no purpose in exposing the dried layer
>to UV.
>IME, a print that's properly exposed and developed is entirely stable
>to rewetting.  If soluble gum is left in the print, in other words if
>the print is removed and dried while there is still soluble gum in
>the paper, then that soluble gum will continue to dissolve and change
>the print when it is rewetted, but if the print is properly exposed
>and developed, there will be no undissolved gum and the print will be
>entirely stable to water, containting only hardened (insoluble) gum.
>If you think about it,  the permanence of a gum print is a function
>of the insolubility of the hardened gum.  If the print dissolves when
>wet, that's not a permanent print.
>
>Katharine
>
>
>On Apr 23, 2010, at 9:41 AM, Paul Viapiano wrote:
>
>>Christina...
>>
>>These are all very good questions.
>>
>>Personally, I like to put down at least two layers before PVA
>>sizing. I have noticed that the layer after the size has a harder
>>time adhering, hence I should probably expose more or develop for
>>less time. But then again, there are so many variables going on in
>>any print, that I haven't taken the time to try and pin it down.
>>
>>I think that someone (Keith Gerling) also mentioned a while back,
>>that he found layers were less stable when re-wetted. Would things
>>be more stable if we exposed the print to UV after drying each
>>layer? Just a thought here...
>>
>>I don't know if the print really sits on top of the PVA any more
>>than the gelatin. I look at it as just helping the already-sized
>>paper along as its original size gets diluted with repeated
>>soaking. This is all very unscientific of me but is what I'm thinking.
>>
>>Paul
>>
>>----- Original Message ----- From: "Christina Anderson"
>><zphoto at montana.net>
>>To: "The alternative photographic processes mailing list" <alt- 
>>photo-process-list at lists.altphotolist.org>
>>Sent: Friday, April 23, 2010 6:31 AM
>>Subject: [alt-photo] Re: IDEA? NEW ALT PHOTO BOOK
>>
>>
>>
>>>Bob,
>>>
>>>I think it could be a good thick chapter of a book...
>>>
>>>I am probably opening up a can of worms here...
>>>
>>>I've been using the Gamblin PVA size now and taught it to my class
>>>this semester in place of glutaraldehyde hardened 2.8% gelatin
>>>(6ml of 2.5% per liter), and it is a great teaching method and
>>>really user friendly.  Boy was my life easier--no hot plate,
>>>massive sizing day, mess, toxicity.  PVA you can just "size as you
>>>go". It is the "magic bullet" of teaching for sure.
>>>
>>>I use it 1+2 on Artistico.   I found more issues with staining
>>>with PVA than with glut/gelatin but that I think is specifically
>>>related to having to determine the dilution of PVA for each
>>>specific paper.  I almost think Fabriano might benefit from either
>>>a 1 + 1.5 or an intermediate layer of sizing between multiple
>>>coats. But at a point, then, PVA becomes too slick and plasticy.
>>>
>>>However, after having worked with it all semester I slightly
>>>prefer glut/gelatin.  **But** I am not sure I prefer the latter
>>>enough to go to all the trouble to do it.  With tray sized sheets
>>>gelatin is no big deal, but with 15x22 size sheets it is a pain.
>>>PVA wins, hands down, for user-friendliness.
>>>
>>>I will be finishing up two large gum projects this summer so we'll
>>>see by the end of summer how I feel--if I go back to gelatin in my
>>>own work, in other words.  I will continue to teach the non-toxic
>>>PVA method, but parts of me think I should still at least show
>>>students traditional sizing because of a concern I am feeling.
>>>
>>>My concern is this:  when I take a print out of the water to hang
>>>to dry, even the border of the print is what I would call
>>>"unstable"--meaning a fingerprint on it will mar it quite
>>>extensively in a way I have not seen with gelatin sized paper.
>>>Anecdotally, a rewetted PVA print SEEMS also less stable--layers
>>>still manipulatable.  Is that an issue?  I don't know. My question
>>>is does each layer you do of dichromated gum on top of a layer of
>>>previously hardened gelatin also affect the gelatin below (another
>>>colloid) and does it, in fact, affect a layer of PVA in the same
>>>way?  Or can the layer of gelatin even GET rehardened repeatedly
>>>with each succeeding layer of dichromated gum or is it hardened
>>>once and for all with the glut and that is it--successive layers
>>>do nothing?
>>>
>>>Or is this just a "hydrophilic" thing, or that gum is (how would
>>>you say) "attracted" to PVA in the same way it is to a surface of
>>>gelatin?  Are, in effect, PVA and gelatin truly interchangeable in
>>>sizing or is it possible that each layer of hardened gum has
>>>better adhesion to a layer of gelatin vs. a layer of PVA, probably
>>>only visible at the microscopic level?
>>>
>>>Maybe the scientists of the list can answer these questions and
>>>put my mind to rest, because my lurking fear is that the gum print
>>>on top of the PVA may not be as stable in the long run as one on
>>>top of gelatin.  A non-scientific test I will do in a couple
>>>months is soak a PVA'ed print and a gelatin-sized print, old ones,
>>>side by side, and scratch and see the results. But I don't know if
>>>that proves anything.
>>>
>>>I hope someone will come on list and say this fear is completely
>>>unfounded, that both sizings create equally stable final prints.
>>>But I am worried the gum print sits on top of the size instead of
>>>melds into it.
>>>
>>>I have no answers, just asking the hard questions....on this quest
>>>for the most perfect, easiest size.
>>>
>>>Now, as far as other processes aside from gum....salt...hmmm....
>>>
>>>Chris
>>>
>>>
>>>Christina Z. Anderson
>>>christinaZanderson.com
>>
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