Re: Gum problem(s)

From: Yves Gauvreau ^lt;>
Date: 11/18/05-11:53:20 PM Z
Message-id: <052801c5eccd$8c127d80$0100a8c0@BERTHA>


I have found a spectral output curve for the photoflood and other
incandesant lamp and the curve shows about a 12-13% relative output at 400nm
and it goes down to 0%, in a near linear fashion, at about 250nm. Someone
told me that the gum dichro as a peek response at around 370 nm. (I don't
recall the exact number) This would mean an output of just above 40 Watts at
that peek.

A factor that could play against the use of photoflood bulbs in the long run
is there relatively short life (10-100 hours) especially if I take 20
minutes chunks out of it each time.

As for the relative humidity well, my very short experience tells me that a
20 minutes exposure at around 30% RH results in step 1 showing a subtle
difference with step 2 (Stouffer 21 step) but this a one time event and
obviously no conclusion can be drawn from this experience. I can add also
that these subtle difference are present all the way to step 8 and 9 then I
don't see any differences subtle or otherwise from 9 and above. This could
mean 20 minutes is still not enough to reach 5 stops.

Katharine experience is that she needs only 2 to 5 minutes at around 55 %
RH. This does not mean much again but it's a substancial difference that I
don't know how to explain and it can't be the distance, the bulb is no more
then 18 inch above the glass.


----- Original Message -----
From: "Katharine Thayer" <>
To: <>
Sent: Friday, November 18, 2005 11:43 PM
Subject: Re: Gum problem(s)

> On Nov 18, 2005, at 2:20 PM, Christina Z. Anderson wrote:
> >
> > Second, I don't think I'd take the humidity thing too far. I have
> > gone from South Carolina to Montana, from 50-70% humidity to now 25%
> > humidity, and my gum exposures are the same. The length of time I can
> > successfully keep a coated and unexposed gum print before it succumbs
> > to dark reaction is probably changed, though.
> 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
Received on Fri Nov 18 23:51:32 2005

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