using Kreen on NuArc

I have a NuArc exposure unit. It has been suggested to me that I try using Kreen instead of the glass on the vacuum frame to help get better contact between my plate and transparency.

So, how do I replace the ‘rigid’ glass and instead use the Kreen, which I believe is a mylar-like flexible material?

Regards, David

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If you aren’t getting good contact in the glass frame, it could because of the way you prepare negatives and plate material, or by the way you operate the vacuum.
The plate material must be trimmed cleanly on all four sides (back-trimmed), or the deformation that occurs at the edge of the material (on the outside of the cutting blade) will prevent contact nearby, and if on multiple sides can act like a gasket trapping air.
Either the plate or the negative should be matte surface, or the negative sprayed with silicon slip treatment, or the plate dusted to reduce tack. If you have slick emulsion film and smooth plate, they may adhere and trap air. Having the negative larger than the plate may be better for drawdown.
You also need to use the vacuum bleed valve, open until the blanket is drawn up to the glass and then slowly closing to get full drawdown. You will see Newton’s Rings between neg and glass then, showing complete contact, and they will also show any dust or hair present.
Krene is a very flexible material, and wears out quickly with use (punctures, deformations), so covering the whole frame will run into a lot of material. You’d need to remove glass and blanket, and replace the blanket frame with a face plate with shallow grooves in it leading to the hole to the vacuum system. Another person attempting this started a thread either here or on yahoo PPLetterpress, but I don’t recall how it ended up.
I used a NuArc 26-1kmercury vapor unit for many years to expose photopolymer plates, but the main problem was not contact, but rather the light source. It isn’t quite the right part of the light spectrum, and is some distance from the frame, so exposures need to be much longer than from the UV tubes of a standard photopolymer exposure unit. As the bulb aged I was getting into 20, 30, even 40 minute exposures for fine detail. And I’d think a NuArc carbon arc unit would be even less efficient.

Thanks for this info. I am doing polymer gravure, exposing my plate first to an aquatint screen they an inkjet transparency of an image to create an ‘etching’ like plate to ink and print.

I dry the plates with a hair drier then apply a thin coat of baby powder. For the screen and transparency, I again dry with the hairdryer and brush with an anti-static brush. I will also pay attention to the plate edges, and may need to adjust the pressure in the unit.

I’m doing 4 unit exposures, so I think the light source in my unit works okay for my use (I believe its a NuArc 26-1k mercury vapor unit).

Best, David

So for photopolymer gravure, you would be working from positives, right? You really need to be careful about dust and dirt then. From my point of view, glass might be preferable because it is so easily cleaned, and the Newton’s rings would indicate the slightest speck under the glass or under the film. Other wise you may get pinhole flaws in the non-image areas.

paraelle_imp, “photopolymer gravure” ungh! To my knowledge you can print relief or intaglio with photopolymer. Gravure is a intaglio process that has nothing to do with photopolymer.
Best james

We have an etching Press for Printmaking and all the Tools to work on copper. The newer crop of clients doesn’t have the skill level any longer to work on copper. They send us pdf’s of drawing done in Photoshop. (Bitmaped).
We helped develop a separation software which allows us to take the PDF and delete the background (papercolor) as this would print as Platetone. A FM based positive Film is made and a polymerplate developed. A copper plate could be etched too, but they don’t care. This is printed as an etching on our etching Press.

james, I was just using the phrase the original poster used, but I have no objection to it. I’ve done traditional copperplate/aquatint photogravure, so I have a little familiarity with the process. But I also know a number of people doing what they refer to as photogravure using photopolymer plates. John Sullivan at Logos Graphics in SF is doing very fine work this way. Thanks to a dithered dot, the results are much finer than photoetchings with a standard screen. You can be a purist and groan, but the results are very good. And no ferric chloride to deal with!