Re: Gum problem(s)

From: Katharine Thayer ^lt;[email protected]>
Date: 11/19/05-12:23:16 AM Z
Message-id: <>

On Nov 18, 2005, at 9:53 PM, Yves Gauvreau wrote:

> Katharine,
> 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.

Interesting, thanks....

> 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.

Still pretty cheap at $5 apiece? But like I always say, I'm not out to
make any converts about anything in gum, only to say what works for me,
and I know the vagaries of gum well enough to know that what works for
me might not work as well for someone working under different
conditions or with different materials.

> 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.

I don't think you're really going to know anything until you see a step
print without the stain.

> Katharine experience is that she needs only 2 to 5 minutes at around
> 55 %
> RH.

Well, to clarify a bit, maybe 4 minutes at 55% and 2 minutes at 85%
(these are guesses, not actual hygrometer (hydrometer?) readings. These
are paper negatives, BTW. With
film negatives (FP4) my usual exposure time in the normal 85-95%
humidity is 1.5 minutes. 5-minute exposures have mostly been for
things like a double-weight fiber-based paper negative.
Received on Sat Nov 19 00:24:06 2005

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