Re: gloy for tricolor on yupo?

Man, I'm really screwing up here...first I don't match my subject line with
my content, even though I was addressing Terry's comment about gum being too
thin in said letter, mind you. Now poor Loris is taken to task for using my
name in vain. I kinda like the sound of "a la Christina"....I always talk
about "a la Sam Wang" so now I feel like maybe I can approach Sam in
caliber.

So in (humorous, tongue in cheek) defense of Loris and myself, let me
clarify:

I do use 15% dichromate, so I am not using a saturated dichromate. However,
my 6 minute time I settled on, down in humid SC or up here in dry MT, is
based strictly on the Nelson PDN system, first finding my standard printing
time with a step wedge, then finding the particular color ink choice that
determines my paper white, and then exposing a step tablet at that time and
with that paper color to plot a custom curve. So it is not an arbitrary
time choice, but one densitometrically chosen.

Since that time (6 minutes) has remained consistent through humidity, color,
you name it, and since Loris and I are both using PDN, it is understandable
that he would say what he said.

The 6 minute printing time, given UVBL and 15% dichromate and my workflow
gives me a layer that develops in an hour and yet can also be spray
developed without the layer sloughing off. It also provides a deep enough
colored layer. At 5 minutes it is not bad either, but the layer of gum is a
bit more tenuous and not as strongly colored--the more exposure, the deeper
the gum layer is and hence the more pigment remains on the paper. At least,
in side by side step wedges exposed at 1, 2, 3, 4, 5, and 6 minutes this is
the case--the colored layer thickens and therefore deepens with exposure. If
my website ever gets up it'll show this little example.

Since I have had 15 students also corroborate this (given a different Epson
printer, different curves, different color negative chosen), I think a 6
minute UVBL print time is within the reasonable scheme of things, using a
half strength/15% dichromate and therefore being kinder to the environment
even if I have to take a minute of extra exposure. But, of course, a 7%
dichromate does just fine with this, too.

One of these days I'll have a few moments to see if the curve is different
for the 7% dichromate, or even for potassium. One of these days I'll even
have time to take my new Epson R2400 out of the box so I can, in fact, print
negatives since my 2200 died. Ahhhhh, so many printers, so little time....
Chris

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, March 30, 2006 5:42 PM
Subject: Re: gloy for tricolor on yupo?

>
> On Mar 30, 2006, at 12:39 PM, Loris Medici wrote:
>
>
>> I assumed development of each layer will take 30 minutes. (I had
>> developed my tests on paper for 1 hour - I expose "a la Christina"; at
>> least 6 minutes - making relatively sturdy layers...) How do you develop
>> so quickly? (Hot water, abrading w/ paint pad or brush, water
>> jets...???)
>>
>
> Sorry, that was a mental lapse; I was thinking of something else when I
> wrote that. I was thinking about a project I'd done that I described
> here recently, where I was coating yupo with pigmented dichromated gum,
> and doing two layers from coating of the first layer through final dry of
> the second layer in less than 15 minutes. BUT, the crucial thing there
> was that it didn't involve an image; there was only one value: DMax (for
> that particular pigment mix) so there was nothing to develop, and it
> only had to be in the water long enough to wash out the remaining
> unreacted dichromated, which really only took a couple or three vigorous
> swishes through the water. The gum layer was totally hardened after a
> few seconds in direct sun, so there wasn't any soluble gum/pigment left
> in the layer to be developed out. So, sorry, bad example. Yes, when you
> figure in developing an image, it would be more like an hour and 45
> minutes than 30 minutes to make a tricolor gum on yupo. Like I said, a
> slight brain malfunction. sorry.
>
> But I must take some mild issue with your statement "I expose ala
> Christina, at least 6 minutes-- making relatively sturdy layers." The
> exposure time required to make "relatively sturdy layers" is a function
> of so many things (light source, negative, type of dichromate and
> concentration thereof, and relative humidity, for starters) that it is
> simply meaningless to state an absolute exposure time that will result in
> "relatively sturdy layers."
>
> My exposure times are almost never more than 2 or 3 minutes, but my gum
> layers are extremely sturdy; I've demonstrated this by pouring boiling
> water on them from a height without disturbing the hardened gum. But I
> use saturated ammonium dichromate and I live in a very humid climate,
> which together probably account for most of the fact that I can print a
> very sturdy layer in a short time. If I were using potassium dichromate,
> or diluted ammonium dichromate, or if I were living in a drier climate,
> exposure times to make a sturdy layer would be longer (and in fact my
> times are longer during rare dry spells here. So, like I say, a
> statement to the effect "I expose x minutes, making a relatively sturdy
> gum layer" is a meaningless statement. With some lights, with some
> dichromates, in some environments, 6 minutes would cook the emulsion to a
> fare-thee-well, while with a very different combination, 6 minutes
> wouldn't be nearly enough to create a sturdy gum layer, and 20 minutes
> might more like it. So, it all depends.
>
>
>>
>> I don't see why dichromated PVA wouldn't adhere to Yupo - I mean when
>> thinking it is used to "glue" things. (Bookbinding, package
>> manufacturing, self adhesive labels...) Of course I'm speculating
>> assuming PVA will be more adhesive than (or equally adhesive as) whole
>> egg (read as temperapring - I know temperaprinters can make as much as 9
>> layers).
>>
>>
>
> Loris, I didn't ask if you thought it should work, I asked if you knew
> anyone who had done it. But I think maybe a couple of things are being
> confused here. As to coating, I can coat yupo with gum easily; the issue
> for me with gum and yupo isn't the adhesion of the coating to the yupo
> but the adhesion of the hardened gum to the yupo, which is a completely
> different issue. (Note: I'm talking about a normal gum coat, not the
> extremely thin dry coats that I recently discovered adhere very well to
> yupo through development but are difficult to coat smoothly. Whereas a
> normal gum coat, in my experience, can be coated quite smoothly but won't
> stick to the yupo through development).
> Katharine
>
Received on Thu Mar 30 22:07:13 2006