RE: red safe light

DEAR LIST,
        All along I thought that salt prints were only sensitive to UV so ANY
source that had the UV filtered out was fine. I believe that is what Ryuji
is saying...yes? Am I wrong here? So why the red safe lights?
                CHEERS!
                        BOB

 Please check my website: http://www.bobkiss.com/

-----Original Message-----
From: Yves Gauvreau [mailto:gauvreau-yves@sympatico.ca]
Sent: Thursday, November 10, 2005 5:29 AM
To: alt-photo-process-l@sask.usask.ca
Subject: Re: red safe light

Ryuji,

assuming we are talking of a UV safe light, any color above the UV range
would theorically work. In reality, most of the materials used to filter out
the UV or any other range of the spectrum, are far from perfect and
especially they don't usually have a sharp cutoff in desired range. You can
visualise this a bit like a graduated filter and the darkest area would be
placed in such a way as to block the UV range (partially) and letting most
of the other colors or frequencies go through barely affected. A good UV
filter would need an effect something like a 8 EV or stops maybe more in the
UV range to work. It all depends on the sensitivity of the material your
using.

The physics of light would suggest that a red translucent material like the
one used on the Home Depot bulb would probably have an effect on the UV
range but maybe it wont be enough. As I said above, the dimming effect of
this specific red material on the UV range isn't known, for example an
infrared sensitive film (IR) also have a similar sensitivity in the blue
range.

A red filter like the Wratten #25 as only about a 10 stop blocking effect on
the UV while a #8 (yellow K2) is blocking even more UV then that.. As you
can see, it's more a question of the response of a material then only it's
color.

Yves

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, November 10, 2005 2:50 AM
Subject: Re: red safe light

> From: Judy Seigel <jseigel@panix.com>
> Subject: red safe light
> Date: Thu, 10 Nov 2005 02:38:21 -0500 (EST)
>
> > (I've also had fogging when my red photo bulb got scratches -- most of
> > them are made with a red lacquer sprayed on top of a regular plain
bulb...
> > which can scratch, flake or crack. I patched with red nail polish.)
>
> Does it have to be red? What difference does it make?
>
Received on Thu Nov 10 07:39:00 2005