Re: Fugitive pigments

Alan Mynett wrote:
>
> Hello David,
>
> I've been using a Philips facial solarium for alt exposures for over a
> year now. Its radiation is UVA (315nm - 400nm) which is the
> 'safest'(relatively speaking) of the three regions into which ultra
> violet light is general divided. (UVB is 280-315nm - causes sunburn -
> and UVC is 200-280nm - this is used in UV sterilisers). Even so, it's
> not safe to look directly at UVA, (and frankly I think I'd pass on the
> intended suntanning role of the lamp!) . It can start the process of
> damaging the eye's lens which will ultimately lead to cataracts in later
> life.
>
> I built a cradle for the lamp to rest on. This puts the bulbs about
> 2inches above my printing frame and prevents any UV light leakage.
> I've been using exposure times of 3 to 4 minutes for both cyanotypes
> and gums - though (very) preliminary test with Mark Nelson's PDN
> suggests that I ought to be using around 6 to 8 minutes. (Sunlight in
> the UK is hardly consistent enough to be of practical use - at least
> for a control freak like me!).
>

Hi Alan-- just to clarify, I wasn't suggesting actually using the sun
for exposure; I was just answering Jan's question about whether the UV
exposure during printing could be enough UV to generate fading of the
pigment, by comparing indoor exposures to sun exposures and suggesting
that the equivalent of a few minutes in the sun shouldn't be enough to
cause even a fugitive pigment to fade. Your exposure times above seem
consistent with my answer; it looks like the facial sunlamp doesn't
print particularly faster than other light sources, or than the sun
itself, so like other light sources wouldn't generate more UV in
printing than 2 or 3 minutes in the sun would.

Generally it takes a day or three of direct sunlight or a few weeks or
months of indirect sunlight to produce noticeable fading even in a more
fugitive pigment. And more permanent pigments take much longer to fade
of course; many of the pigments we use are available to us because they
are bought in large quantities by car manufacturers and vinyl siding
manufacturers (a bit of trivia: quinacridone gold is no longer
manufactured because it wasn't popular as a car color); these pigments
are tested for months and years of direct sunlight. (That's a more
complete answer to Jan's original question than I gave the first time
around.)
Katharine
Received on Tue Jul 26 05:09:46 2005