Another UV Light Box (16x20)

[drewf64]

Can't speak for Jim, but I've done a fair bit of salt and albumen printing with mine. 20 minutes is not unusual (mine was based on one of Jim's designs, has a bank of 12 fluorescent BLBs) but of course it depends on the negative and the particular sensitization formula you use. It's the usual story: print until it looks good, then print a bit longer. If the border starts solarizing/turning metallic looking, you're pretty much there.

Exposures should be roughly the same for salt vs. albumen; after all, it's basically the same process, just with some underlayment in one case, so to speak.

Robert

Hello Robert:
Thank you for your reply ... very helpful.
Are you using 1 inch BLB lamps?
UVA 352nm or 368nm?
17 inches long?
What size are your negatives/printsThanks!
Drew

[denverjims]

Drew,
I had seen builds using BL as well as BLB. I had not remembered hearing/reading that one was better by any substantive amount. I think I said that my decision was based on finding a deal on the bulbs I used. They seem to be adequate.
As far as sun vs box, I never used sun. My understanding is that, even at our altitude, the box beats the sun by a fair amount. I'm getting old and did not have the time to wait for the sun. :>)
Best, Jim

[Jim Noel]

Drew,
I had seen builds using BL as well as BLB. I had not remembered hearing/reading that one was better by any substantive amount. I think I said that my decision was based on finding a deal on the bulbs I used. They seem to be adequate.
As far as sun vs box, I never used sun. My understanding is that, even at our altitude, the box beats the sun by a fair amount. I'm getting old and did not have the time to wait for the sun. :>)
Best, Jim

I believe you have that reversed. The sun is usually faster than fluorescent tubes. In my case in Southern Cal, printing in the sun is exactly one stop faster on a normally sunny day.

[Robert Brazile]

Yes, the sun is generally faster, assuming it's not 4PM on a winter's day. :-)

As to Drew's questions: I'm unfortunately on the road again today, so can't go peek at my unit and give you the specific specs. A photo of the underside of the unit, which may help, is here: https://flic.kr/p/hWR7Ks

I'll look at it again when I get home to refresh my memory. I will say that I never did know the exact frequency profile of the lights but to date I never have needed to. The bulbs came from Home Depot; I haven't seen them there in a while, so they may not carry them any longer, but I expect can be ordered easily enough. I believe they were intended as aquarium lighting.

The archives of the carbro list may have some information on the bulbs; I originally built the unit to do carbon printing (and it works fine for that) and Sandy Moss has mentioned his findings in testing these there a few times...

Robert

[drewf64]

Robert:
Thanks for the photo. Looks to be one inch diameter tubes and this matches the specs for T8 in your photo and the other descriptions in this thread.
17.xx or 18 inches long depending on which manufacturers' ruler we use!
I am now shopping around for the best deal on BL or BLB tubes as it looks and sounds like the 352nm vs. 368nm UVA wavelength issue is a NON-issue.
As much as I would prefer to use the sun, if I can get predictable and repeatable light output from the box I will be very happy!
Again ... Thank you.

Jim & Jim:
Thank you for your replies ... appreciated!

Drew
Drew

[denverjims]

...
As much as I would prefer to use the sun, if I can get predictable and repeatable light output from the box I will be very happy!
...
Drew

I guess I had the wrong understanding about the sun vs box re: speed. But, frankly, the factors you just mentioned would have had me go to the box anyway. Not to mention the fact I can print in the evening or on heavy overcast days.
Best, Jim

[jp]

With the sun, you can guess or use an integrator to measure exposure as brightness and UV changes. Quick bright exposure will work different than slow gradual exposure; the slow exposure will self-mask to a certain extent and have a slightly different contrast at least with cyanotypes as the coating changes color and starts to reverse with time part way through the exposure. As such I think an indoor exposure box is most predictable. Perhaps run it for a minute before using it to make sure the bulbs are all up to temp and happy. When I print, it's usually bad weather outside or 9-11pm (after the kids are in bed.)

[Robert Brazile]

The box is definitely more consistent and therefore predictable than direct sun, although an integrator helps with this. With respect to contrast, even in full sun you can affect this by using sheets of tracing paper as a diffuser over the printing frame. Holds back the shadows while the highlights develop, then once you get them where you want them, you can pull the tracing paper to get to final density. Works well.

Robert