Re: Gum problem(s)

From: Katharine Thayer ^lt;>
Date: 11/23/05-12:21:45 PM Z
Message-id: <>

Who knows, but I wondered about that. I don't have any of those
gadgets, but I dry my coating with a hairdryer always, and I dry it
until it "feels" right (once it's dry enough to touch, I run the back
of my hand lightly over the coating while still holding the dryer on
it with the other hand, until it feels perfect; this takes just a few-5
to 10 I'd say--more seconds). I was thinking when we talked about
this the other day that since I dry my coating to the same perceived
driness no matter what the RH, that you'd think my times should be the
same regardless of the RH. And to be clear, I don't make day to day
changes in exposure; my times are pretty much the same most of the
time, but then the RH is pretty much the same most of the time. But
when there is a rare dry spell, I do have to increase my exposure

It's been sunny for the last week or ten days, after weeks of endless
rain, so you would think it would be dry enough that I would need to
extend my exposures now, but that wasn't so on Saturday when I ran off
a quick print on cardstock for a friend's birthday card; it printed in
one minute, which is the standard time for that set of "negatives"
(BTW, if anyone is interested, these aren't actually negatives, they
are rubbings I made on tissue paper some years ago which print great as
negatives for gum prints; I make note cards from them and people who
get my notes always tell me that they frame them). That's the only
printing I've done during this nice patch except for a couple of quick
tests, because I can't stand being inside while the sun is shining,
after such a long period of no light. But the air doesn't feel
particularly drier than usual, it feels just like it always does. So I
checked online for the local humidity just now--- 95% even though it's
a crisp sunny morning, 33 degrees F. (That's cold for here). So no
wonder there's no difference in exposure time.

I don't know if that clarifies or confuses the issue, at any rate
that's how it is for me in the damp northwest. And now it's Judy's turn
to chime in and say you shouldn't ever dry your coating with a hair
dryer. (I noticed a few months ago, when I was busy doing something
else and let the mail pile up, that when I went back to look at it, all
I needed to do was look at the topics and the names, and I knew exactly
how the whole discussion had gone without even having to open the

Now I need to decide what I'm making for a salad for tomorrow, Bye,

On Nov 23, 2005, at 12:46 AM, wrote:

> I'm not a gummist, so you can take what I say with a grain of
> salt—either pottassium or ammonium dichromate....
> I always monitor my PT/PD printing with a hygrometer and adjust the
> RH in the coating and drying room (my smaller bathroom, but that
> doesn't sound that professional) using a humidifier.  What I find
> equally important is to monitor the drying time, since that affects
> both the amount of moisture in the coated paper and coating as much as
> the RH.  Is it possible that you may each use a different combination
> of drying time that would cause variance in RH to make a difference in
> one case and not in  the other? 
> OK... back to my closet.
> Mark Nelson
> Precision Digital Negatives
> In a message dated 11/22/05 7:04:56 PM, writes:
> hmm. Maybe it doesn't make so much difference at a lower dichromate
> concentration, or something; at any rate I do have to adjust my
> exposures for changes in humidity-- like when there's a dry spell
> after
> a long rainy season, I have to expose longer.  Not 20 minutes,
> certainly, but another minute or two. But even when it's dry, the RH
> here is seldom below 50-60%.
> I don't know how else to account for the fact that my exposure times
> are so short with the photoflood, than the humidity  of my
> environment,
> along with the established link between humidity and exposure required
> for hardening. How else would you explain it, unless the idea of long
> exposure times with photoflood is simply a myth and not based on
> actual
> observation?
> But this may just be one of those things we'll have to agree to
> disagree about.
> Katharine
> Mark Nelson
> Precision Digital Negatives
Received on Wed Nov 23 12:22:31 2005

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