[alt-photo] Re: Can I convert a light table to UV light source?

[Judy Seigel]

On Thu, 12 Aug 2010, Phil wrote:

> Can I convert a light table to UV light source by just replace 24" or 48" 
> regular light tube with BL or BLB light tube the same size and use as a UV 
> light table/box?
>
> Usually a light table has 2-4 tubes. Will the UV light power might be enough?
>
> Let's say the light box has 4x48" tubes, how long time it takes to expose a 
> cyanotype prints? My regular mid-day cyanotype takes 12-24 minutes.


In my experience, a light table configured for viewing transparencies 
works well with the plain light bulbs a few inches apart.... but for 
exposure (such as cyanotype) they should be close enough so you don't get 
hot spots. And the closer the paper, obviously, the closer the bulbs have 
to be.

I don't work extremely large (IMO more trouble than it's worth), but my 
cyano exposures range 10-15 minutes... this of course is affected by how 
far the bulbs are from the image, how close they are together, the density 
of the negative, the density of the cover glass (I also found exposure 
varied depending on the glass itself & its thickness. And a shocker in my 
first class -- discovered, finally, that a previous teacher used glass 
guaranteed UV proof, which was of course why nothing came out !), how long 
the emulsion has been on the paper (after 1 day it gets slower), also (I 
assume) the chemicals themselves -- how fresh they are, and all the other 
variables of paper, humidity, coating, negative density, etc. (Some papers 
are --- I forget what they call it -- something like "pH neutralized")... 
and I wouldn't recommend them for cyano, or anything else, for that 
matter.)

But if you're working with familiar, relatively fresh emulsion, and known 
paper....just don't look directly at those bulbs for longer than 
necessary. Plus, maybe 48" bulbs are possible to avoid? ( Harder to handle 
& waste of electricity.)

(Someone on the list -- or maybe everyone on the list but me -- will 
remember what the BLB -- or blacklight blue -- bulbs are for, but my 
recollection is, again, they give less light & cost more, also are 
slower.)

J.