U of S | Mailing List Archive | alt-photo-process-l | Re: spots and dots and UVBL solarplates

Re: spots and dots and UVBL solarplates


Christina Z. Anderson wrote:
Good morning all,
I've been thinking about this dotty discussion...it's interesting that I have never noticed a spot discussion on the list until after MONTHS of discussing it re: solarplate, and then FINALLY it comes out that other processes have this issue. Several of you, e.g. Sandy King, have it. I wish that it was mentioned way back when, Sandy and others, that you had this issue with other processes, too, because that would have helped narrow down the culprit much more quickly (and saved me big bucks).
Hey Chris,

I think it was several years ago I asked about it on the list and Jan was the main one who responded to me and ID'd the newton rings (maybe a couple others too). Since that time I've been on a long path away from the standard approach, solving problems, introducing others, solving them again, bit by bit until coming up with the procedure I published on-line last year. Jan was onto the right solutions too when he advised I dry the OHP with a hair drier and using baby powder. I just wasn't drying it long enough. Don't feel bad about blowing plates. I share that burden and have easily "wasted" a couple grand on materials in the past 3 years testing and tweaking...which is why I published my notes and workflow which at least a few people are following as a starting point. Plates are recyclable at places that accept scrap metal. :-)

I have never seen this with gum so assumed it was a characteristic of photopolymer only until others came forward. I also assumed that it was a factor of UVBL in combination with photopolymer and then come to find out the spotty issue continues to plague those with expensive point source lights. So, if the spots are truly just Newton Rings and a factor of the top side of the transparency in contact with the glass also, that seems much more manageable in the long run--see what the list can do if we take the time to share? Maybe we should spray the top side of Pictorico with Krylon?

One last thing about spots--if these plates are used for computer chips (am I not mistaken?) then the computer industry has GOT to have solved this problem...
Most industries now print direct to plate avoiding the transparency step entirely.


But my real question is this: why has UVBL been considered a bad source for photopolymer, that point source is better if, in fact, the spot issue still is a factor with point source? I cannot see anything wanting in my UVBL images, except the spot issue. I can see that when the aquatint exposure is too great, the image becomes mushy (Susan, like your step wedge image at the bottom of your blog), but if the aquatint screen and the positive are in a 2:1 to let's say 1:1 the images are sharp and tonal. Until I get that ol' Amergraph I won't be able to do a side by side to see the dif, but what is it I might expect when switching to point source that will "wow" me?
Chris

I've never ID'd why UVBL is a problem precisely, and stopped worrying about it once I got my Olec, but do know that a diffuse light source causes weaker shadows (take, for example, florescent lights in a classroom). Compare that to the shadow created by a point-source halogen lamp or even incandescent light. During screen exposure, this light-source, and shadow created from it, affects the shape and sharpness of the aquatint dots. Weaker fuzzier dots are still dots, but I believe create, on a very subtle level a slightly weaker, fuzzier, print. Since most point sources also come with a vacuum frame, this solves many of the dark spots and patch issues relating to poor contact which, according to Dan Welden and others, is the single most prevalent problem people have with this process.

Especially with larger plates (16x20"), the problems with UVBL becomes notably worse. I have a colleague who use tubes (tanning bulbs, I think) but only for small plates. Large ones were so problematic under UV tubes they use the sun now for those.

I think an easy test would be for you to try the sun...or borrow a friend or colleague's exposure unit to see the difference.
Been exchanging Email with a guy at Pictorico who said they're in the process of developing a matte OHP product which may solve all these problems (though maybe not the newton rings on the bottom of the glass (kreene > glass)). The solution of taping double-sided frosted mylar to the bottom of the glass sounded like a good one. Has anyone doing poly plates tried that yet?

Best wishes,
Jon