RE: BL vs BLB tubes for cyanotype

Hi Charles,

> Loris and Sandy,
> I was more surprised than you at the 3 minute exposure. My first

> test strip was 8,9,10,11,12,13 minutes--all overexposed. So I did
> another at 3,4,5,6,7,8 thinking that perhaps I was mis-reading

What do you mean by overexposed test strip? Do you mean every steps were
equally dark?

BTW, before having a Stouffer target, I was making my test strips by
exposing in half stop increments (gradually covering paper at the
following timings: 01:00, 01:25, 02:00, 02:50, 4:00, 5:40, 8:00,
11:20...). I was determining the exposure time by looking where two
consecutive steps are equally dark (checking with reflected light). Most
of the time, I would notice one more step in transmitted light (read as
light table) but since the difference was not visible in reflected light
(usual viewing conditions) I was omitting this extra step.

> the 8 minute test. My homemade unit is very simple. It has 6
> type F15T8 bulbs on 90 mm centers and places the bulbs about 95 mm
> above the glass of the contact frame. The glass is standard hardware
> store glass sold for window replacement.

Your current setup should be giving less UV than mine - I use 40W 24"
tubes, 40W electronic ballast for each, lamps are just 40mm above the
glass of the frame. Frame glass is ordinary 2mm glass. But my exposures
for obtaining dmax are longer than yours (I need about 1.5 stop more
exposure for maximum density). That's why I thought you may be not
getting the maximum density capable with your sensitizer. Of course our
formulations may be different, I use the classic cyanotype formula given
in the C. James book.

Regards,
Loris.
Received on Wed Nov 16 02:19:02 2005