UV exposure unit question

Hi all,

I built a UV exposure unit as described in "the new platinum print."

I made the unit with 8 bulbs (I'm doing 4x5s) and I used the GE

blacklight bulbs described in the plans (they're the white kind, not

the ones you see at parties). The problem is this: the exposure

times are l-o-n-g. In a variety of contrast formulations, with the

developer at 110 degrees, the exposure times are right around 20

minutes. At first I thought that the negatives were just

bulletproof, but I used a stouffer step wedge and if I print for 20

minutes, steps 1-4 are black. If I print for 15 minutes, steps 1-3

are black, and if I print for much less, there aren't any pure blacks

in the prints.

Is it the bulbs? Does anyone have any suggestions? The exposure

times are supposed to be ~5 minutes...

Thanks in advance.

A. What's in your emulsion? (Translation: Did you use any contrasting agent?)

B. What film/developer did you use? High base fog + pyro stain could mean long exposure times.

C. 20 minutes is within reason. One of my negatives takes 10 minutes, one takes 50. I use a different light source than you, but some difference from others' tests is to be expected.

I am building a box from the same plans, but am using 12 lamps. Dick Arentz suggested I use SA lamps (super actinic) as having a better spectrum (higher intensity for the desired wavelength range). They are 20W each. I cannot tell you how long the exposures will be yet, but I expect shorter than what R.S and C.W. report in their book. It is possible to go to a 75W S.A. lamp, but I would imagine the transformers to cost a small fortune.

Greg Nelson

How far is the negative from the bulbs? what developer are you using?

If you are using ammoinum citrate, just change to potassium oxalate and your printing times will be 10 mins, which are normal.

If you can and want to reduce printing time, get the negative closer to the tubes.

You might want to look at my article on UV light sources at http://unblinkingeye.com/Articles/Light/light.html

I am not at all convinced that the SA lights are better than BL for platinum printing. You will find conflicting opinions on this from some very expereinced alternative printers.

I collaborated with Dick Arentz last fall in testing printing speed with platinum using a variety of light sources and the results of that test are at the site noted above. The results of my tests indicate that the BL tubes are in fact more effective than SA tubes for platinum.

Sandy King

I also built a UV unit based on the design in "The New Platinum Print" with eight 20W BL bulbs and my usual exposures for Pyrocat-HD developed negatives are in the 20-30 min range. I may try to retrofit to 75W SA bulbs to perhaps speed up the exposure.

Some of my very dense negatives, like one ice pattern photo, which I print with a lot of contrast agent, take up to 1.5 hours to properly expose.

FYI,

I'm using equal amounts of Pd and Pt, and equal amounts of sensitizer A and sensitizer B (the normal one and the restrainer). I think the actual numbers are 6 drops of each or something. The bulbs are about 3 inches from the print.

20 minutes isn't necessarily too long.

Bob Lane

The tubes just don't have enough power.

<br>Wouldn't it be better to use a 400w Metal Halide lamp instead?

<br>Lots of red light which you don't need, but, it's very strong in the blue spectrum.