Re: A little gum test

>
>If your windows are closed, there will be practically no UV light at all.
>This might suggest you actually expose your gum layers at - visible -
>blue/violet radiation (which in fact would not be too surprising given
>dichromated
>colloids are sensitive from UV - ~550 nm)...

I question your statement that if the windows are closed there will
be practically no UV light at all. Ordinary crown window glass
transmits a very high percentage of UV radiation over 350nm, and some
UV even as far down as 300nm.

It is true that colloids have some sensitivity up to 550nm, and
radiation at this wavelength could expose a gum print. But it would
take a very, very long time. My opinion is that in the situation Kate
describes a lot of the radiation is indeed in the UV range below
400nm, especially considering the relatively short exposures she
describes.

Sandy King

>
>Martin
>
>----- Original Message -----
>From: "Kate Mahoney" <kateb@paradise.net.nz>
>To: <alt-photo-process-l@sask.usask.ca>
>Sent: Monday, December 15, 2003 8:49 PM
>Subject: Re: A little gum test
>
>
>> What's really interesting is that I NEVER use direct sun - all my prints
>are
>> exposed in a corridor with high windows which reflects a lot of light -
>but
>> I think the UV must be high because digital shots in the area always come
>> out very blue on daylight setting. You would hardly think that 4 min
>> exposures in diffuse light would be overexposed!
>>
>> Kate
>>
>> ----- Original Message -----
>> From: "Katharine Thayer" <kthayer@pacifier.com>
>> To: <alt-photo-process-l@sask.usask.ca>
>> Sent: Monday, December 15, 2003 1:09 PM
>> Subject: Re: A little gum test
>>
>>
>> > Kate Mahoney wrote:
>> > >
>> > > Hi Mark, Less contrast with the saturated solution was
>> > > postulated....so I'thought I'd give it a whirl. I have been getting
>> > > rather flat prints so this is good news. The results (to me) show some
>> > > of the reason why I've been having some trouble with this technique -
>> > > obviously too much amm.di. I think the reason why the tones are better
>> > > is that mostly I've just been overexposing with the amm. di. at the
>> > > more concentrated level...
>> >
>> >
>> > Thanks Kate, this provides some confirmation for a suspicion I've had
>> > for some time, that when people say that saturated ammonium dichromate
>> > prints flat, perhaps what they really mean is that they overexpose when
>> > they print with saturated ammonium dichromate. I have never observed
>> > that saturated ammonium dichromate prints flat when properly exposed.
>> > That not only the shadows but the highlights were blocked (I'm assuming
>> > you mean after a reasonable development time) suggests that the problem
>> > was related to significant overexposure, as you suggest above, rather
>> > than to the contrast range of the saturated dichromate per se.
>> > kt
>> >
>>
>>
>>
Received on Tue Dec 16 00:55:17 2003