UV light sources for cyanotypes - some newby questions.

[mrtoml]

I have just acquired a Philips solarium to use to expose cyanotypes. I have done a search and found widely different guidelines for timings and distances (anything from 55 seconds to 30 minutes and 1" to 12" distance from the negative).

I am thinking the best bet will be to try a kind of maximum black (or rather maximum blue) test with a few strips of paper and a blank negative say starting at 6" distance and exposing for longer and longer as one would with an enlarger and paper. Does that make sense to anyone to establish a base time?

My second question concerns the maximum size of print. If you pull the lamp back far enough (it has 12" tubes) could you conceivably expose an 11x14" print with a suitably longer time. That is the maximum size I would ever intend to go (and not for a good while yet). Does the inverse square law apply to UV?

My final question concerns making my own unit. Can one use ordinary fluorescent units with black light bulbs? I have some 24" aquarium fittings but don't know whether it is OK to put UV intense bulbs in place of the normal aquarium lights.

Thanks.

 

[Robert Hall]

The size, type, and distance will all play a roll in your exposures. You will have to do some testing and what you propose sounds like a good way to start.

It might be a bit more quantifiable if you had a step wedge, but Cyanos are not terribly expensive so a few tests shouldn't put a damper in your wallet.

On the max print size, you will simply have to test and see what light fall off you have with your unit. The light falls off as a square of the distance so print times will increase quickly, so yes, it does apply.

On your last question, as long as the tubes can match the ballast, which sounds to be the case, you can use black light bulbs. Many Aquarium bulbs are in fact, UV intense, as you say.

If you really want to shorten times, find a HID grow light and ballast. Here in the states I've seen one for about $180 which would do a bang up job.

Best of luck

 

[yeknom02]

Re: your last question: I have built my own exposure unit by putting in unfiltered blacklight bulbs (BL as opposed to BLB?) Anyway, they appear frosted white when switched off, so think of tanning bed bulbs rather than college dorm room bulbs.

I'm 99% sure that as long as the bulb wattages are similar, you're not going to run into any problems. I wired together all my fixtures and they all work fine when I turn it on. I haven't yet tried printing anything with it, since I am very lazy and I am trying to figure out how far above the paper I want to put the bulbs so I don't get any lines of varying exposure.

 

[mrtoml]

Thanks for your replies.

I have found it very difficult to gauge maximum blues from a test strip and can see that extending the time does not print the lighter shades from a negative before the shadows block up. I guess changes in the negative generation regime are necessary.

At least with the solarium I can get reproducible results so a big step forward.

 

[banana_legs]

Hi Mark,

If you are using traditional magnetic ballast (that uses a little starter thingy) to drive the lamps then you should have no problem with swapping to UV tubes. If you are using electronic ballasts however, beware as they are *very* specific to a given tube type. The UV tubes I am using do not work in some electronic ballasts designed for equivalent white-light tubes; the operating and striking voltage of the UV tubes is higher and therefore the over-current protection in the electronic ballast tends to trip out before it can strike the lamps.

Best regards,

Evan

 

[mrtoml]

Thanks, Evan.

I have been looking into this more and think it would be better (and probably cheaper) to build one from scratch rather than try and adapt my aquarium lights. I'll need more ballasts anyway. So I am looking at getting 6 or 8 18" T8 tubes (F1ST8-BL) and 3 or 4 double ballasts.

Does this sound OK for doing up to 11 x 14? What is the advantage if any of using (more) T5 tubes?

 

[largeformat pat]

I made my box from white shelving and fitted 4 twin 600mm (2ft) tubes. I have felt feet bellow and a handle at one end. made mine big enough for 16x 20 cost about $120.00

 

[largeformat pat]

I meant to also say sorry for the quality of these, I just raced done and used the phone. I also just use the power point to control my times. I've found 3-5min a starting point for my salt prints.
Pat

 

[mrtoml]

Thanks, Pat. That is really useful. So I should be OK with 8 tubes and 4 twin ballasts.

 

[largeformat pat]

I just brought the twin fixtures and that is how they come. I ordered the UV tubes from my electrical wholesaler, the fluro twin battens are sold with two standard tubes. many spares now for my encapsulate safe lights.

 

[John Weinland]

Cheap UV

You can spend as much as you like for professional features but hardware-store-type screw-in UV bulbs work fine and cost (locally) about $6 USD each. You will need three for an 8x10 printing box suitable for platinum-palladium work. (I don't know about cyanotypes). Put the bulbs in a milk-crate (available from chain stationery stores) on the bottom, line the crate with aluminum foil, and place your printing sandwich above the crate, face down. Works fine, no fans, ballasts or starters required, and exposure times are only a bit longer than commercial-grade equipment. (About 4-7 minutes instead of 3). The bulbs are 7-watt units and a conventional Gralab can easily handle the 21-watt power load. Total cost about $35. Fancy timers, vacuum frames and other conveniences are very nice to have and may be worth the extra expense for what you are doing. Email me for a series of jpgs on how to construct the thing.