Re: Roller for gum (was: Re: humidity in your darkroom........

Gum is not hard to coat...or, that's the least of my worries.

A couple authors in books said they didn't print in the summer because their
prints were "muddy" which I presume to mean either lower contrast, or
perhaps a higher incidence of staining possible, even, because of the
increased receptivity of the paper to more moisture (Livick being one).
Livick also says in his book to dry emulsion for 1/2 hour to 45 min, no
longer, or emulsion will start to set in the paper and highlights will be
muddy. Blacklow says don't print in high humidity because the dichromate
soaks up moisture from the air and become less sensitive--either that is her
conjecture or she got it from someone else. Crawford says heat and humidity
increase dark reaction. Arnow says gum is not very sensitive when wet
(Gassan, Kosar, and others disagree) and in higher humidity, use a shorter
exposure--the seeming contradiction possibly being explained away by dark
reaction, perhaps? So, the humidity factor is out there in the lit and in
practice but what exactly is true, your guess is as good as mine.

Coming from Montana, a semi arid place where I don't think the humidity ever
gets anywhere CLOSE to what it is down here in the winter, even, I did have
an adjustment to make, and that is that my paper took longer to dry either
naturally or by hair dryer, and it never "snapped" like my paper in MT (plus
you don't leave dishes in the sink in water here...mould occurs)(but my
hair's nice and fluffy! Maybe that's why "big hair" is still in fashion
here).

That said, I never saw a difference in outcome that I could relate to that
one variable, so I filed that concept in my "Possible Gum Myth" folder.
Then again, if those authors have fine tuned their process to such a degree
and print the same image over and over, so they know if there is a miniscule
change, perhaps they're wiser than I--well, that's a given. But humidity in
this case could be one variable among many, like something new in the water
during summer, or increased temps which made their dichromate solution
stronger, or change in manufacturerer paper sizing, or whatever. In other
words, there are other changes that could cause gum changes aside from
humidity in the summer.

Chris

> Ender100@aol.com wrote:
> >
> > I don't do any gum yet, but I wonder if humidified paper would lead to
> > easier coating?

In my experience "humidity" is not a thing, it's a relative... toggled by
heat and AMOUNT. that is, I find staining and fogging occur in high heat
humidity, but hard to GET same humidity when it's 25 degrees cooler. some
advisers say you can coat smoothly if you wet the paper. I found that this
gave almost total staining... Even dampening back of the paper in areas
left stain.

So IME any generalizations about humidity in gum printing tend to be only
from one patch of the elephant.

I'd also agree with, I think it was katharine, that coating isn't such a
problem as all that...And a gum coating that LOOKS uneven before exposure,
may print perfectly evenly... In this I suspect you're confusing gum with
pt/pd... which is a VERY bad mindset for gum.

J.
Received on Sun Jan 18 09:07:36 2004