[Alt-photo] Re: Mechanism for Platinum Enlargements

[Don Sweet]

Somebody raised this question years ago, and as I recollect the accepted
wisdom was that a solar powered enlarger (as contrasted with a "Solar"
enlarger) was impractical because the lens would block too much uv light, or
overheat, or both.  If that is true, then another way of making the sun's
rays diverge might be to use a slightly convex mirror as the light source,
with the remainder of the enlarger inverted over that.

Don Sweet

----- Original Message ----- 
From: "Francesco Fragomeni" <fdfragomeni at gmail.com>
To: "The alternative photographic processes mailing list"
<alt-photo-process-list at lists.altphotolist.org>
Sent: Wednesday, November 06, 2013 6:40 AM
Subject: [Alt-photo] Mechanism for Platinum Enlargements


> Hi All,
>
> I may have asking something along these lines a long while back but I'm
> unsure. There also may have been a bit of conversations around this
on-list
> in the past. Anyway, I've always been fascinated with the old methods for
> making Platinum enlargements and I'm curious if anyone knows any of the
> numbers (exposure times) or knows of anyone who's working (albeit slowly)
> with anything like this now.
>
> Despite common belief, making platinum prints through an enlarger is
indeed
> possible and there is a long history of this. As a quick recap, the most
> common method was through the use of a solar enlarger attached to a
> heliostat. The solar enlarger was essentially the same as a modern
> enlarger, most commonly using condenser lenses but there is documentation
> discussing diffusion solar enlargers as well, and lenses that were good at
> passing UV light. The heliostat was a mechanism that allowed the enlarger
> to track the movement of the sun subsequently keeping the light source
> centered and focused throughout the printing.
>
> Much later Durst made a UV enlarger for Azo and supposedly had one in
> development for platinum printing but it never made it into production.
>
> Anyway, I've heard whisperings of people who's made platinum enlargements
> essentially in conventional enlargers after replacing the lens with an
> older lens that'll pass uv light (modern lenses tend to block uv) but I
> can't really find any documentation of this. What I've heard is that the
> super powered lamps as used in the Durst UV enlarger (5kw and requiring
> serious cooling) are not actually necessary if you're ok with loooong
> exposure times (into hours). The Durst was supposedly designed to make
> these exposures both possible and relatively quick. I personally wouldn't
> care if the exposure times were very long if this is something that could
> actually be achieved.
>
> Does anyone have any information/experience with this? Any idea of how
long
> exposure times would actually be if using a uv bulb or mercury bulb in a
> diffusion or condenser enlarger?
>
> Lets try to keep this on topic. This isn't intended as an opening for
> recommendations to contact print or make enlarged negatives. This topic
> isn't concerned with any alternatives. We're all aware that platinum
prints
> are conventionally made using contact printing. We also know about making
> enlarged negs. No need to touch on any of that here. This is about the
> feasibility, practicality, and possibility of making a platinum
enlargement
> via an enlarger set up to utilize uv light. We're also not tied to
> attempting to attain short exposure times here. Long is fine. I'm
> interested in tapping into the creative thinking of those on-list so lets
> try to limit the "thats impossible" talk. We already know that platinum
> enlargements are possible. Thoughts?
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