Re: Sizing paper with gum and dichromate

Hi,
I haven't sized with dichromated gum, because I didn't want to bother
with the extra steps of exposing and developing the paper before you'd
even coated it to print; seemed like a lot of extra work to me. I did
try a brief experiment of sizing with gum hardened with glyoxal, and
got good and bad results with it, for reasons I didn't have time to try
to sort out. At any rate I like the glyoxal-hardened gelatin mix that
I use and don't have any particular reason to change.

But this confirms my observation that treated dichromate stain turns a
greenish color.

Again, I haven't claimed that stain is purely a function of exposure,
in fact I've made no claim about why I get clear gum and others don't,
when printing with unpigmented gum. But the clear gum that I get is
very hard; it doesn't go soft with application of water, takes some
effort to scrape off a hard surface, and the same area of it fills the
same volume as unstained gum (I don't have a scale to weigh that small,
so I had to look at the volume of the scraped gum rather than the
weight, to determine that *for me* exposing to the point of staining
didn't give me more volume of hardened gum, the gum was just more and
more stained, and more and more crystalline. Very stained gum scraped
off the surface looking like coffee grounds compared to the unstained
gum, which scraped off as a film of translucent materia. I found this
all very interesting.

It's probably not as simple as differences in dichromate, even more
than I think it is as simple as differences in exposure, but I could
imagine it being an interaction between dichromate and light sourcet,
or dichromate and gum, or all three and more.

The chemist I've been working with speculated once that perhaps some of
the differences we see in practice may have something to do with
different wavelengths that we're using to harden the gum; perhaps gum
behaves differently at different wavelengths. Since, as I reported here
a couple of months ago, there's evidence that gum responds at
wavelengths shifted considerably toward green from albumen's
sensibility spectrum (I wish they had used gelatin as a comparison
instead of albumen) and since my photoflood is probably using mostly
visible wavelengths, maybe gum just works like this for me because it
is a better match to gum's actual sensitivity spectrum. Who knows? I
don't, and I'm getting weary of trying, as Judy says, to eff the
ineffable.
Katharine

On Dec 20, 2005, at 8:31 AM, Kees Brandenburg wrote:

> Chris,
> I just finished some testing on this subject. I coated several sheets
> of BFK (because I had some leftovers). I mixed my gum (homemade from
> lumps) and dichromate (saturated pot.di) as I allway do in my
> pigmented mix. My usual printing time (UV fluorescent) is 4 minutes.
> I coated 6 sheets and exposed for 4, 2, 1 minute and 30 and 15 sec
> (all through a piece of blank Ultrafine Crystal Clear film). After
> that I left the paper 'develop automaticly' in the water for 1 hour
> (as I allways do) and dried. The next day I cleared (at least tried
> to) the samples in 5% metabisulfite.
>
> Conclusion: all but one sample had the green stain. The 4,2 and 1
> minute exposed had a severe stain. The one that stayed white was
> exposed for 15 sec. (i.e. 4 stops under normal). The 30 secs sample
> was acceptable allthough stained. Than I coated another one and
> exposed for 30 seconds and left this one in the water overnight. Next
> morning it looked much better than the first 30 sec. sample.
>
> Next step will be coating these 15 and 30 sec samples with my usual
> pigmented mix and look how they behave compared to gelatine sized
> paper.
>
>
>
> -kees
>
>
>
> On 20-dec-2005, at 17:06, Christina Z. Anderson wrote:
>
>> Good morning,
>>
>> I'm late on replying to this post but so it goes at Christmas...
>>
>> My problem with sizing with gum is this: in order to get the layer
>> hard enough to be a suitable size, there will be some discoloration
>> with the dichromate that stays in and discolors the whites, in my
>> practice. So by experience I agree with kees. If I didn't harden to
>> the point of discoloration the layer was too soft. I tried clearing
>> with pot metabi but that whole procedure seemed like so much more
>> work than just biting the bullet and brushing on a hardened gelatin
>> size (e.g. two separate wet and dry cycles). Even so, the layer did
>> not prevent staining.
>>
>> But I would assume somewhere someone out there has luck with this
>> method who is perhaps using lighter pigment loads, although my
>> assumption is also that since this method, quoted in the books long
>> ago, never caught on as primary practice means it just isn't as good
>> as a plain old hardened gelatin size. You know what they say about
>> "assume", though...
>> Chris
>>
>> Probably a much short time will be enough then. But maybe
>> the break even point of hardening enough before the staining starts
>> doesn't even exists.
>> kees
>>
>> Loris Medici wrote:
>>> Hi Kees,
>>> But you will still omit the density of the pigment that way...
>>> Regards,
>>> Loris.
>>> -----Original Message-----
>>> From: Kees Brandenburg [mailto:ctb@zeelandnet.nl] Sent: 15 Aralık
>>> 2005 Perşembe 16:26
>>> To: alt-photo-process-l@sask.usask.ca
>>> Subject: Sizing paper with gum and dichromate, was Re: glut
>>>
>>>
>>> ...But why not standardize things a little bit more and size with
>>> gum and expose with your standard printing time through a clear
>>> sheet of printing substrate (or film). I'll give that a try this
>>> week...
>>>
>>>
>>
>>
>>
>
Received on Tue Dec 20 12:20:36 2005