Hi Mark,
I think you and I discussed this at some point. Is it
newton rings? I guess by definition it is. But I think Chris and
Susan's circumstances are different, as are the demonstrated effects,
and their possible solutions, respectively.
I think in Chris' case, it's uneven contact between the screen and/or
image and the plate during exposure. I've seen more severe weirdness
when using black light bulbs too, which for some reason I have never
been able to explain, seemed to contribute to the patches -
particularly with larger plates (larger than 8x10). I think part of it
has to do with the fact that a greater surface area makes it more
difficult to maintain consistent contact. I rarely see problems of
this nature from plates made using a point source -- such as the sun --
even with larger (16x20" plates). The sun is, of course, not as
precise as the timing and output of a BLB light box, but I typically
see less mottling from printmakers who use the sun -- especially when
they go 8x10 or larger.
In Susan's case, again, you can see the same effect clearly illustrated
using a virgin sheet of OHP and a virgin KM73 plate under a vacuum.
Technically it's also newton rings, but I think the solution for her is
going to be different, since she's using the KM73 plate under Pictorico
OHP. Solarplates, as it turns out, do not have this problem with OHP
since they don't have a protective mylar sheet sealing in their juices
-- and it's made out of different stuff, with a slightly viscous,
rather than the tacky feeling to its surface as the KM73 plates have.
Solarplates do, however, generally arrive with more surface
defects...just the nature of the beast. They also hold plate tone more
aggressively, making them, in my opinion, more suitable to graphical
printmaking as opposed to photogravure. We've of course seen the
exceptions...
Here's an example from my procedure of the effect more like what
Susan's tests are showing:
http://www.lytescapes.com/procedures/polymer_photogravure.html#trouble
Unfortunately, I don't have any examples looking like Chris' since I
abandoned all that data (and the approach using BLB and Solarplate)
long ago. But the feelings of seeing the effects again are like it was
yesterday (if I happened to be incredibly ill with a cheap vodka
hangover yesterday, that is)...hehehehe
Check's in the mail Mark. ;-)
Thanks,
Jon
Ender100@aol.com wrote:
Jon,
Is this a manifistation of Newton Rings?
In a message dated 2/20/07 12:25:28 AM, jon@terabear.com writes:
Measles...good analogy.
Notice the difference though. Chris' measles are dark in the light
areas, while Susan's are white in the dark areas.
Chris: http://czaphotography.com/img/learning/solarplate/Guncompare.jpg
Susan:
http://bp1.blogger.com/_K_E_8kwTNvw/RdqEKwry8dI/AAAAAAAAAA4/trtOOQWlZ3g/s1600-h/radish01.jpg
My .02 cents/sense is the causes are related, but are manifested for
different reasons. I've suffered through both of them. Both have to do
with uneven contact during exposure, as you may have guessed.
Susan, however, unlike Chris, is using a vacuum frame. Contact should
be flawless, right? Wrong. Why, has to do with the "tackiness" between
OHP and the KM73 plate which was documented in my procedure. Took me
about a year to figure this problem out, but my excuse is I had to go
between Boulder and Denver once a week to actually print the tests, like
Chris. But, I'm not as bright as her either.
Susan: If you want to test this, take a virgin KM73 plate with the
mylar removed, and a virgin piece of OHP (without an image printed on
it), sandwich them under the vacuum frame and hit the switch on the
vacuum. I'll bet you see a similar, but subtle pattern of patches
manifesting like leprosy within the first minute of drawdown. The
aquatint screen, unlike your image transparency, is made of real film
and doesn't have this issue, but the OHP is tackier against the KM73
plate and this is the problem. The remedy for me has been baby powder,
very lightly dusted over plate with a hake brush (Jan gave me the idea
several years ago). If you were using baby powder, the other key is to
not let the image exposure draw down too exceedingly long. I basically
wait until the Krene goes flat against the bed, then hit the exposure
switch with no extra drawdown time beyond that. Since the screen
exposure is not the issue, you can draw down on it as long as you want.
I do things in this order:
Remove mylar
Expose Screen to plate
Dust plate with baby powder
Expose Image to plate (minimal drawdown time)
Washout normally
Hope that helps.
I've got some other things I'm testing out to help with the OHP issue
with the KM73 plates and will report back if I come up with anything
better than the above.
Best wishes,
Jon
Best Wishes,
Mark Nelson
Precision Digital
Negatives - The System
PDNPrint Forum at Yahoo
Groups
www.MarkINelsonPhoto.com
|
