Re: Fugitive pigments

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!).

-- 
Best wishes
 Alan                            
http://www.mynett.org.uk
Monday, July 25, 2005, 7:55:49 PM, you wrote:
> 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!