Re: continued solarplate notes
Yeah, I know...this was with point source.
I remember the big ol' convo we had on this years ago.
Chris
----- Original Message -----
From: "Sandy King" <sanking@clemson.edu>
To: <alt-photo-process-l@usask.ca>
Sent: Sunday, April 08, 2007 11:13 AM
Subject: Re: continued solarplate notes
I am not sure what type of light source folks are using, but inverse
square law of light does not apply to UV tube banks, only to point
and collimated light sources. Increasing distance from 4" to 8" with
a bank of BL tubes may increase exposure times a bit, but not
anything close to a factor of 4.
Sandy King
At 8:09 AM -0600 4/8/07, Christina Z. Anderson wrote:
Well,
I finally received my Fotogravure book by Eli Ponsaing after it made
a circuitous route to SC and back to PhotoEye and then to MT...
A couple interesting tidbits that I could glean from the English
part of the text (most is in another language):
1. PHP suppliers say sensitivity depends on temperature, the best
being 25C/77--colder is slower.
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").
3. After development Ponsaing post dries the plate at **50C/122F (!
Shades of Keith) for 10 minutes either in a warming cupboard or a
hair dryer, and then post exposes.
4. He inks on a hot plate (never done that--don't know why I would,
but I do cut the ink with Easy Wipe).
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.
I find it fascinating that he is first exposing the positive. That
is next on my list. After spending all last weekend in the
printmaking lab I was ready to put solarplate away for a while, but
you know, Jan Pietrzak, I think we should all make APIS a goal to
share our photopolymer images! Maybe a panel presentation, Dick
Sullivan?
I know most people are busy with famdam on Easter weekend but
thought I'd share it when it is fresh in my mind.
Chris
|