U of S | Mailing List Archive | alt-photo-process-l | Re: Light source

Re: Light source

thanks for pointing out other possible cause for the unevenness.
I perfectly understand that one can consider a short exposure time itself as a cause for unevenness but let's say we have a large area of light uniform tone on our original, I'm sure you would want it light and uniform on the print. Your negative would need to have a relatively high uniform density in this area, right? As you probably know, within certain limits, you can control exposure by varying either time or density. I could have suggested to use a negative with a uniform and relatively high density for this test, instead I choose to vary the time by about 3 stops to produce the same effect, I think 3 stops is well within the range of carbon.
----- Original Message -----
From: ender100
Sent: Thursday, July 24, 2008 12:07 PM
Subject: Re: Light source


Not unusual to get uneven tone when making short exposures with some materials.  It may be the light showing uneven coverage, but more likely variance of speed of the emulsion itself.  For example, with PT/PD, it could easily be variances in moisture in the emulsion.  For carbon—perhaps moisture, perhaps uneven sensitization.

Best Wishes,

Mark Nelson

On Jul 24, 2008, at 10:12:39 AM, "Yves Gauvreau" <gauvreau-yves@cgocable.ca> wrote:

this may interest some of you.

While testing for exposure time with a friend, we realise that something was
let say bizarre and we decided to test our light source. We exposed for 1/10
our standard exposure time to obtain a mid to light gray. We made the test
print the same size as our usual prints using no transparent materal.

As soon as we could see the result, (carbon print) we where stunned, there
where major differences in tone all over the print and all sort of
undesirable artefacts.

We where using a point source and decided to try an UV tube bed instead and
of course we will make another test just in case.

The lesson learn from our experience may be useful to others and I thought
we should share it with you.

Yves and Philippe