Re: continued solarplate notes

[Jon Lybrook <jon@terabear.com>]

\Christina Z. Anderson wrote:
> 2.  Exposing is done in 3 stages--main exposure first for **15** 
> minutes with the light source at 1/2 the distance of the aquatint 
> exposure. Aquatint exposure SECOND--**15** minutes with the distance 
> of the light 1 1/2 the diagonal of the vacuum frame measure.  Post 
> exposure 5 minutes. (on a Stouffers dark steps 8, 9, and 10 should be 
> "clearly defined").
Maybe he's using a maglight to make his exposures.  ;-)

> With the inverse square law of light 1/2 the distance of the positive 
> means it is 4x the length of exposure, correct?  So Ponsaing's ratio 
> of exposure is 4pos/1aquatint.  Can you believe the length of his 
> times??!!  I can't read the text to see what his light source is, 
> though, unfortunately. I can glean that he is using Japanese plates KM73.
>
> Oh, here are his light choices:  "uv lys, kviksolvdamplampe hpr 125, 
> drosselspole bhl 125 eller l44, metalhalogenhampe, xenon lampe. And 
> then Ikke alle lyskilder er egnede til vor kopiering.  Der kraeves 
> lysbolgelaengder mellem 400-360 my i det ultraviolet-te omrade af 
> spektret. Ved anvendelse af FP-plader til dybtryk, er punktlys bedst 
> egnet, d.v.s. at lyskilden har sa lille en udstraekning som muligt.  
> Dette lys findes i kviksolvdamplampe, hojfjeldssol, xenonlampe, 
> metalhalogenlampe og kulbuelampe.
>
> My interest in the light source choice is to compare his longer 
> exposures with what we are doing with KM73s.  What he is doing is 
> still not disproving my theory that the length of exposure is not as 
> crucial as the ratio, unless, say, he is using REALLY weak bulbs which 
> I don't think is true--I can at least decipher halogen in there. But 
> it still supports the theory that, like gum, the longer exposure (to a 
> point) the thicker the layer of goo on top of the substrate, whence 
> comes Welden's description of the forgiving latitude of exposure of 
> the plates, that exposure is not so crucial.
So based on your theory Chris, if my ratio is 1:1 screen/image, I could 
do 10 seconds/ 10 seconds, or 1min/1min, or 15min/15min and it wouldn't 
make a huge difference?  This might be true to some degree if one is 
using imagesetter film for both, since the density of imagesetter film 
is so heavy.   I'd expect the dots would change size as time is 
increased though, since the longer exposures would allow more light to 
sneak underneath the edges of the dots.  Easy enough to test

Thanks for the posting!

Jon