U of S | Mailing List Archive | alt-photo-process-l | Re: continued solarplate notes

Re: continued solarplate notes

Well, results of two tests, for whatever it is worth:

I proved to myself my theory holds water. I did a solarplate at 8 mn aquatint/8 mn positive in full on direct HOT sun. I normally expose solarplate 3.5/3.5 to 5/5 under 15 watt UVBL. I got a perfectly beautiful tonal range of 7 stops from white to black.

Considering that Mike Ware says the sun is several times more powerful than UVBL (anyone know the exact comparison?) this is enough proof to me that there is a quite wide range of acceptable exposure and that the ratio is where it's at.

I exposed a KM73 plate to 8 minutes (!) aquatint but cut the positive exposure to 3 mn to relate to my 2 mn/45 ratio I found under UVBL with this plate (haven't tried the 49/41 ratio outside yet) and sure enough I got a usable image, although a bit on the bland side. Same hot sun, direct sun, but the deepest black on it corresponds to 1 stop less black than the solarplate deepest black. This stands to reason since my solarplate exposure is usually 2.5 to 3.5 more than the KM73 plate exposure. To have a range of exposure from 49sec/41sec UVBL 15 watt to 8mn/3mn outside full sun is a pretty dramatic indication of latitude.

Interestingly, I don't see a (dramatic or otherwise) difference between the sun exposed plates and UVBL, yet, anyway. I got four Newton ring spots still even though I powdered both sides of the screen and positive and the top side of the plate.
The end,

----- Original Message ----- From: "Jon Lybrook" <jon@terabear.com>
To: <alt-photo-process-l@usask.ca>
Sent: Sunday, April 08, 2007 5:25 PM
Subject: Re: continued solarplate notes

SusanV wrote:
Jon, the Dan Weldon screen isn't that dense at all.  I'm getting the
same exposure times as you are, adjusted for my 1000k lamp.

Hi Susan,

You may be getting the same exposure times at different wattages, and but we're also using very different screens. 80% density indicates coverage of dots (dpi), not density of the "tone". Every dot is 100% opaque - at least that's how the plate should see it with a proper screen. Both our screens may have "80% density", but the exposure times (and perhaps ratios) between them will vary using the same light source. Are you doing the exact same screen/image times as I am? If so, it could be worth examining, or could be coincidence...I don't know.

Another thing about longer exposure and the undercutting of dots...
that's not really the same as a finer screen.  The dots would be
smaller, but they still number the same per inch so the space between
would just be larger.
That's true, but I'm suggesting it's similar in the end result. Undercut dots in the screen exposure would lower the density *effect* of the screen on the plate from 80% to something less than 80%,. In both cases the dots are smaller, which is what allows more shades of gray to be produced. There's certain to be other differences...of course. My point was if that particular author was getting good results using our plates with 1K exposures for 15 minutes, Chris may well be correct that the exposure times ratio is more important than the actual times, BUT I'll bet he gets better results than others using lower exposure times (assuming the ratio is the important thing) because his dots are smaller. Just an idea. Difference between 10seconds and 15 minutes for the same media is quite a variance...