Tooth and consequences: Yupo

From: Katharine Thayer ^lt;>
Date: 11/14/04-07:31:57 AM Z
Message-id: <>

Hi All,
I unplugged myself from the list yesterday so I could get back to a
project that I've been neglecting; I apologize for dropping out of on
ongoing debate but will try to catch up later if there's anything I need
to respond to; anyway I've pretty much already said what I know from
experience about tooth.

In the meantime, I had ordered some paper from Daniel Smith and because
they have a minimum order of 10 sheets of loose paper and there weren't
10 sheets of paper I needed to order by the sheet, I ordered a piece of
Yupo just for the heck of it, because I've always wondered what it was
like, and because it was cheap. So when I was unpacking the paper order
into my flat file, it occurred to me that this Yupo would be a good
thing to check my understanding about tooth. And besides, I wanted to
check, one more time, my answer to Giovanni about gum not hanging onto
gelatin.. My experience has always been that if you've got a surface
that's too slick to start with, sizing that surface isn't going to help;
the gum won't stick to the gelatin much better if all than it would
stick to the slick surface in the first place. But since Galina prints
gum on glass by sizing with gelatin, that certainly isn't a universal
rule, and so I was curious what would happen if I sized a piece of
Yupo. I found that sizing the Yupo did not improve its ability to hang
onto the gum, which frizzled and flaked off the surface. When I sanded
the unsized Yupo to give it some tooth, the gum adhered to the surface
well. I used 320 grit sandpaper, which scratched the surface too much;
the scratches were visible in the final print, especially when viewed at
an angle. The only finer sandpaper I had was 600, and I found that that
didn't scuff the surface enough to make the gum adhere.

The main message I want to convey here, believe it or not, is that I
found the Yupo a very interesting material to work with. It doesn't
behave anything like paper; for example I found that exposure times
didn't correlate well with my previous exposures with paper, and the gum
coats on the Yupo very differently than it coats on paper, or even on
mylar. But I also think that if a person were to spend some time with
this stuff, one could learn to use it with gum and get some very
interesting results. And it's very cheap, $1.88 per 20x26 sheet.

Then I had a brainstorm: I thought hey, this might be a quick way to get
Joe's RGB-CMY comparison that he was so determined that I should do for
him: if I used an image that would print well at a small size (the
callas I made separations for before are too subtle in tonal gradation
to print well either small or probably on a hard surface either, so I
used a different image) and printed both types on the same piece of
Yupo, I should be able to finish the six separations in a very short
time; since I know from experience that gum on a nonporous surface dries
very fast, I should be able to do the whole thing in less than an hour.
So I did this, but the result was not very successful. Even sanded, the
Yupo can retain at best two color layers, it seems, so neither the RGB
nor the CMY print kept the cyan layer except in selected spots, mostly
where the yellow and/or magenta negatives masked that area so the cyan
was the first layer or second layer to actually print on that spot.

And of course the other thing is that the two sets of separations are so
different that it doesn't make sense to do them with the same exposure
and development. So if I were to do this comparison seriously, I would
need to make two separate prints, an RGB print and a CMY print. From
what you can see of the flawed prints, the RGB looks better than the
CMY, but that's because of course the CMY separations are less dense and
so need either less exposure or more development or both to turn out; it
doesn't work to do them on the same sheet as the RGB.. So, as I say, I
wouldn't take ANYTHING from this failed comparison, except to note how
the gum prints on the sanded Yupo.

At any rate, as I've said before, the question of whether RGB or CMYK is
better isn't very interesting to me. The way I look at the RGB-CMYK
thing, if you're used to RGB separations and know how to use them, then
you will get good results from RGB separations, and if you're used to
CMYK separations and know how to use them, you will get good results
from those. As I've said before, I don't think there's a right or wrong
on this, and I think it would be very difficult to establish some kind
of accurate judgment of whether RGB is inherently more accurate than
CMYK or vice versa, since so many other things go into the final color
balance: pigment choice and how the pigments behave in combination with
each other, skill in printing, probably even the gum used, etc etc etc.
So I don't think this is an issue that can be resolved, and since I
don't have time or energy for the things I really need to do, I don't
put a real high priority on adding more data one way or another to this

Here's the URL for my experiments with Yupo:

Since I wasn't setting out to do a test or demonstration to prove
anything to anyone, I used different negatives and pigments, whatever I
needed to use up a bit of at the time. My goal isn't to set out a rule
for all the gum worlds, but just to show how things work in mine, as
Katharine Thayer wrote:
> Hi Katharine,
> Then, how do you theoretically explain when you print gum on top of glasss
> or alluminum?
> If you don't size it you can't get the image on the gum.
> Glass and alluminum are perfectly clean without any "tooth" and you can
> print perfectly on them, right?
> Giovanni
> ----- Original Message -----
> To: <>
> Sent: Friday, November 12, 2004 6:54 AM
> Subject: Re: Help with what I believe is a hardening issue
> > wrote:
> > >
> > > I have being reading this thread and seems to me that there is a major
> > > confusion.
> > > The purpose of hardening is to the gel not to the paper.
> > > The gel is going to carry the pigment colors meaning the image,
> obviously
> > > the gel is on top of the paper but it can be on top of anything.
> > > Does anyone disagree with me?
> >
> >
> > Hi Giovanni,
> > In my gum universe (which appears in many respects to be a parallel
> > universe to some other gum universes, but that's what makes the study of
> > gum so endlessly fascinating) the gel is on top of the paper, as you
> > say, but the gel isn't what the gum is hanging onto. If you looked at a
> > cross section of paper through a microscope, you would see fibers
> > sticking up off the surface of the paper. It is those fibers, which we
> > call "tooth," that the gum grabs onto and that keep it from floating off
> > the surface. If sizing is so thick or heavy that it clogs up the tooth,
> > then the gum coat will flake off the paper because there's nothing for
> > it to hang onto. Gum doesn't "stick" to sizing; it sticks to whatever
> > tooth it's got to hang onto in the substrate. My 2cents, and as I say,
> > this applies only to the gum universe I know,
> > Katharine
> >
Received on Sun Nov 14 15:28:02 2004

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