Re: Fugitive pigments

I haven't tried a sun exposure, the sun here isn't reliably bright :-) , but
my thinking was based on the fact that I'm using a facial sun-lamp as a
light source, which comes with fairly stringent recommendations as to
maximum use. Even allowing for over-cautious manufacturers this suggests a
higher UV exposure (at the distance used) than they expect you to get from
the sun. It would be interesting to know which wavelength of light is most
active in causing the gum/dichromate hardening reaction - one for the
chemists to think about! Do we all use UV just because it's the easiest way
to get a suitable light intensity, or is the UV itself necessary? I'm pretty
new to alt process so my sorry if I'm asking silly questions!

Jan

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, July 25, 2005 11:44 AM
Subject: Re: Fugitive pigments

> David & Jan Harris wrote:
> >
> > Given that watercolour pigments are affected by light, and when we
expose a
> > gum print we expose the pigments to a lot of UV; probably more UV light
than
> > a watercolour print probably gets over a period of a year; will some of
the
> > pigments already have faded by the time we have finished a gum print, or
> > would more occur later? I know this will vary with different pigments,
but I
> > am interested in the general rule. Do manufacturers test the pigment by
> > intense exposure to light (or UV)?
>
> Hi Jan,
>
> Interesting thought, but I don't expect the amount of UV a gum print
> gets in exposure would be very significant with regard to fading. It
> depends on the light of course, but in my experience most lights we use
> indoors take longer exposure than direct exposure to the sun does, so I
> would deduce from that that in general, exposing a gum print with
> whatever light would give it the same or less UV than exposing it
> directly to the sun for the same amount of time. Certainly a few
> minutes exposure to the sun shouldn't cause any noticeable fading.
>
> Katharine
>
Received on Mon Jul 25 12:53:29 2005