hi, i was wondering... could a uv bulb or lamp of this kind, be used in the enlarger, if the bulb could fit the socket of the enlarger? is it possible? my enlarger is an antique, Fuji Enlarger AII... i'm extremely curious with albumen process... and want to try it... but my negative is only as small as 35mm and 120 type... so, i cannot use the more common method of just applying the negative directly over the sensitized paper...

-- weird ems (emeechua@tri-isys.com), October 13, 2000

Answers

Common window glass, the thick condensers used in enlargers, and most enlarging lenses, will all stop a good deal of UV getting through (almost all of it in fact). Enlarging lenses start to cut light at about 400nm, barely into the true UV region. Simple 3 or 4 element lenses are better than expensive six element ones for UV transmission, but still not good.
Plastic material, such as Perspex (Plexiglass) stops UV almost dead. Fused Quartz glass is the only material that is transparent to UV.
So if you're trying to use a process that needs UV to expose it, you should really be looking at a glassless system, or spend a rake of cash on Quartz glass, or be prepared for very long exposure times.
Sorry, but that's the Physics of it.

-- Pete Andrews (p.l.andrews@bham.ac.uk), October 17, 2000.

Further to the above:
The solutions used in commercial processes that need UV exposure are as follows:
1)Final size negatives or positives are always made, then used for contact printing.
2)Tensilised Polyester based sensitive materials are used for the final artwork, since these have reasonable UV transmission properties, and good stability.
3)Where Quartz glasss is impractical or uneconomic, materials are held in contact by a vaccuum frame and a thin plastic membrane of UV transparent plastic. (a tensioning system is sometimes used instead of vaccuum.)
4)UV exposure units are either of the 'point source' type, or consist of large area tubes or multiple bulbs in open reflectors. (no glass).
That's how it's done in industry.

A cheap source of hard UV is a 'sterilising bulb', used for sterilising hairdressing implements and the like. They're small, low voltage bulbs in a quartz envelope that only need a very simple ballast circuit to operate them. The UV output goes up to 235nm, so eye protection is needed when using them.

-- Pete Andrews (p.l.andrews@bham.ac.uk), October 17, 2000.

how do you used a color enlarger machine to proccess a prints?

-- andy xiong (andyxiong74@hotmail.com), February 02, 2001.