Hi

Can anyone tell me why printing on Pt/Pl "must" be contact sheets? When using 35mm film, can I use a 'normal' enlarger if I replace the light source by an U.V. light source? E.g. I have a Durst 605 enlarger that holds bulb lights. There are also U.V. bulbs, so can I use these? Or doesn't the U.V. light travel through the condensor/lens?

regards Reinier

-- ReinierV (rvlaam@xs4all.nl), May 21, 2002

Answers

You can print a pt/pd print using a 35 mm negative. It's just that the print will be about 24 x 36 mm!

This question comes up about every six weeks in this forum. Here are two real good reasons why.

Pt/Pd emulsion is UV sensitive. UV light is not visible to the human eya. You can't focus a negative. This of course, assumes that your enlarging lens will project UV light accurately.

Exposure times. My contact prints can be exposed from seven to 45 minutes with a bank of fluourescent tubes about two inches away. Now factor in your inverse square law for illumination, and the relatively power of an enlarger light source, and your print exposures are well into hours. It would be impossible to have a completely motion free enlarger/print combo rock steady and solid for that length of time.

You can use your enlarger to make enlarged negatives and then you can contact print your platinum prints. There are a lot of good sources on platinum printing on the internet. The new Bostick-Sullivan site is very good and Mike Ware's alternative process pages are full of answers to your question on Pt/Pd printing.

-- Joe Lipka (joelipka@earthlink.net), May 21, 2002.

Hi Joe

Thanks. I think everybody who starts with interrest in this topic will end up here, A great knowledge base. So an UV source in an enlarger will never be powerfull enough to make useable exposure time.

Thanks, saves me expirimenting. I will check out the sites, I already knew Boston&Sullivan ofcourse :-). I recently ordered a book that explains how to make enlarged contacts on a computer. Sounded like interresting reading material to me.

Reinier

-- ReinierV (rvlaam@xs4all.nl), May 21, 2002.

If you try to mount a UV lamp in your enlarger, be first sure to have the fire brigade waiting in front of your house. And have it insured beforehand, in any case they don't succeed to put out the fire fast enough...

-- George Papantoniou (papanton@hol.gr), May 22, 2002.

The problem is not one of safety. It's simply that the optical system of an enlarger (the lens and condenser or diffuser system) just won't let very much 'hard' UV pass through it. The Platinum process needs UV of a short wavelength, shorter than 350nm, and ordinary glass absorbs strongly at wavelengths shorter than 400nm.

To Joe: I think you'd find your exposure times would be greatly reduced if you used quartz glass in your contact frame. Unfortunately, large sheets of quartz glass are very expensive.

-- Pete Andrews (p.l.andrews@bham.ac.uk), May 22, 2002.

Pete, and what about transparent polymers, like plexiglas? As far as I know it does transmit UV? It can be scratched easily, but it not expensive..

-- Andrey Vorobyov (AndreyVorobyov@hotbox.ru), May 25, 2002.

Perspex, as we call it over here, absorbs short wavelength UV about as strongly as glass. Most plastics do the same. Glass has the advantage, because it can be made thinner with a greater rigidity, and the absorbtion is directly proportional to the thickness.

One commercial way of UV contact printing is to use a very thin flexible sheet of polyester or polythene, and a vacuum frame. The vacuum pulls the sheet down hard over both the neg and the print, and so applies atmospheric pressure to push them into the necessary close contact. The plastic sheet need only be a fraction of a millimetre thick if used in this way.

-- Pete Andrews (p.l.andrews@bham.ac.uk), May 30, 2002.