I am using an old Nu-arc 40-1K Mercury Exposure Unit.
My exposure for Puretch is between .9 and 1.3 units on the machine. It is in the range of 21 sec. ± 3 secs. depending on how long the bulb takes to warm. (for reference the normal exposure for ImageOn is 6 machine units.)

I have had inconsistent results with the exposures. Does anyone know if the bulb's performance wears out before it burns out? If so what is the normal life of the bulb with moderate use? Could it be failing to produce consistent UV and still activate the sensors in with total light? Lastly, is my exposure so close to it's minimum exposure, that I'm up against its margin of error? I don't have control over the maintenance of this device but could lobby for a new bulb.

Thanks for any help

danl

Dan,
I have used one of these at University and maybe can advise.
I'd say that you should def. get a replacement bulb. The bulbs do lose their strength in time. The same thing happened to me and it was so much better when the bulb was changed. The other thing I did before this happened and I got the bulb changed was to run my step tests using a sheet of thick black paper to mask the light, while the bulb warmed up.
I switched on the power, and waited for warm up , then pulled the paper out to time it. Thats a more efficient way when you ar'nt sure if the warm up is right. Although it does sound as if Nik has solved this in a better way.
I also think that you have to run step tests to match your light source, not to match the type of photopolymer you use. Of course its time consuming but worth the results. everfree

Danl, have you tried testing the Nuarc with Puretch with a Stouffer step guide?
This is a great little tool for standardizing exposures. It sounds like your integrator may be faulty. I had to give up on my integrator and let my bulb warm up with the plate covered, then uncover at full brightness and go by counting seconds. I use a 1K Nuarc mercury vapor unit and expose from 7-10 seconds.

The stouffer is just under $10 and can save you a lot of head scratching and film.

http://www.capefearpress.com/stouffer.html

Jennifer

Jennifer,

Great info about the integrator. I believe it is the source of my problems. Also, no one at the facility I use can tell me the normal life of the exposure unit's bulb. It hasn't been changed in a year, which seems like a long time when we have screens and cyanotypes being exposed for 20-30 minutes each.

Yes, I use a Stoufer, one I bought from you. (I thought you would recognize me by my original questions) I gather from your post that you are controlling your exposure unit by hand. In an exposure of 7 sec. being off by 1/2 a sec. is 7% of the exposure, which I would imagine to be significant. Have you found it easy to be within that margin of error and, if so, how?

Thanks

danl
(dan loewenstein)

Hey Dan, I had forgotten you got a Stouffer.
This film has a pretty good exposure lattitude, meaning it can tolerate a bit of variation in exposure. With my light source, I get a 6 or 7 on my stouffer between 7 and 10 seconds. This was from tests done months apart so this shows how a light can change over time and it is good to test with the stouffer every now and then. If you are going to try the manual route, I suggest testing with the stouffer fairly regularly but you should be able to get a system that will work even if the bulb is not as bright as it used to be.
Good luck,
Jennifer