Re: BL vs BLB tubes for cyanotype

You might want to run the bulbs for 50-100 hours before doing any
calibration work. My impression is that you get a slight boost in
radiation from brand new tubes that levels off after about 50-100
hours. This may also explain some of the increase in printing speed
you are seeing.

Also, you should also be seeing a very slight increase in contrast
with the BL tubes compared to the BLBs. It won't be much but the
difference could also make a small difference in printing speed.

Sandy

>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 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.
> The ballasts and first set of bulbs were surplus from American Science
>and Surplus, sold as "party lights." I bought 6 of them, took them apart
>and glued the sockets on one side of a piece of standard hardware store
>shelving material (plastic coated pressed wood fiber.) I screwed the
>ballasts on the other side and drilled holes for the wires. I prop the unit
>on two matching cardboard boxes. As simple as I could make it.
> I assume the original bulbs were slower than the normal BLB bulbs and
>that is why I got such a dramatic difference.
> It sure is nice to have a 3 minute turn around instead of a 15 minute
>one.
>Charles Portland OR
Received on Tue Nov 15 15:18:49 2005