Newton, NuArc and OHP

Yes. The bad part is that the 'improved' version is all that is available in 24" size rolls. I'll figure a way to make this work, but it is a pain in the butt.

sanking said:

Is this Pictorico?

Sandy

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clay said:

Okay, I am getting this damned Ultra OHP calibrated, and I have the same problem with the Newton's rings. The old stuff doesn't do this, only the 'improved' version. Neither do film negatives or imagesetter negatives. One thing that I tried that helped some (but not completely eliminating them) was to take a hair dryer to the negative and drive as much moisture out of it as I could right before printing.

I could really learn to hate this Ultra Uber-improved Radically New Miracle OHP film.

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Clay, same here... I'm ONLY getting this problem with the new "IMPROVED" (my ass) pictorico. I'd prefer to have the old pictorico on a 13" roll instead.

I'm getting the rings with "regular" sheet Pictorico OHP, and I also get it with imagesetter negs. With my gravure process I have to make 2 exposures, one with my ohp positive image, and one with an imagesetter random dot screen... so I have a double whammy of rings to deal with.

Sandy... I'm very surprised the mylar and ohp surfaces meeting didn't cause rings. If this does work it would be a simple fix to tape a piece of sprayed mylar permanently to the underside of the glass. That approach would cause less diffusion of the light source than using frosted mylar, which would be a good thing to my way of thinking. Please let me know if you find out anything further about this technique.
Krylon makes a Crystal Clear Acrylic coating #1303 that adds about 1% density according to Jon Lybrook who tested it recently. He used 2 light coats I believe. He was using it on the inked surface of the OHP though because we were trying to eliminate large air pockets between the ohp and polymer plate. It worked for that purpose. He has since switched to talc and preheating the inked ohp with perfect results, fwiw.

my studio time is limited right now, but I'll do my best to get some testing done this week and report back.

Susan

I just realized that there is an image on my blog that shows how Newton's rings look on my final gravure prints... use the link below if you're interested, and scroll down to the image of the radishes titled "midtone measles". I didn't know at that time what was causing them, but now I know they're the result of the rings between the glass and ohp.

susan

SusanV said:

I
Sandy... I'm very surprised the mylar and ohp surfaces meeting didn't cause rings. If this does work it would be a simple fix to tape a piece of sprayed mylar permanently to the underside of the glass. That approach would cause less diffusion of the light source than using frosted mylar, which would be a good thing to my way of thinking. Please let me know if you find out anything further about this technique.

Susan

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Hi Susan,

The satin polyurethane surface applied to the mylar appears to have completely eliminated the problem of newton rings for me. The satin surface gives a slight tooth which seems to break the interference pattern caused by the reflection of light between the negative and the mylar.

The 3 mil mylar has UV blockage of about log 0.05, or 1/6 of a stop, which should not be much of a problem. The satin coating adds very little to the UV blocking. Some have UV blocking so you should avoid those.

Sandy

Sandy,

where can one get these supplies? i'd like to just get a sheet large enough to cover 16x20 or so and tape it to the underside of my vacuum frame.

Jeremy said:

Sandy,

where can one get these supplies? i'd like to just get a sheet large enough to cover 16x20 or so and tape it to the underside of my vacuum frame.

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Hi Jeremy,

I buy the thin mylar sheet from Light Impressions. Since I use it for other purposes it is something I generally have on hand in 16X20" and 20X24" size. There are many other sources for it I am sure.

Sandy

Jeremy... a good art supply store should have mylar sheets, either by the sheet, or in bound pads of various standard sizes. be sure to get the clear variety... not "matte" or frosted.

Sandy... Thanks!!! This sounds great, and so simple. The BEST kind of solution.

Susan

so where should i pick up this "satin finish polyurethane?"

sorry for so many questions! i grabbed a stack of 0.05" mylar from the art store and there were a bunch of different choices in sprays at a range of prices so i figured i would just ask. i tried spraying PrintGuard on the mylar to see if that would work (as i already had this on hand) and it just made a mess so back to the experts....

Jeremy said:

so where should i pick up this "satin finish polyurethane?"

sorry for so many questions! i grabbed a stack of 0.05" mylar from the art store and there were a bunch of different choices in sprays at a range of prices so i figured i would just ask. i tried spraying PrintGuard on the mylar to see if that would work (as i already had this on hand) and it just made a mess so back to the experts....

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Spray-on polyurethane is available at virtually any home supply store, in both satin, semi-gloss and gloss finishes. The satin finish worked for me, with just one light coat, but I suspect semi-gloss would also work.

I would avoid the brands that advertise UV resistance.

Try to hang the mylar vertical when you spray since it is easier to get a smooth application this way than if it is in horizontal position.

Sandy

Thanks a great deal, Sandy. I'll try to pick some up and report my results back.

I used the suggestion of some of the polymer gravure printers on the alt-photo list and sprayed a very light even coat of Krylon #1303 Crystal Clear acrylic on the back side of a Ultra OHP neg. Negligible effect on the UV density, and it totally eliminated the Newton's rings on the vacuum frame glass. It gave a faintly grainy appearance on the back of the negative, but nothing could be seen in the print, probably because the stuff is so damned thick.

I did the spraying by taping the negative inkside down to a piece of cardboard and tilting it nearly upright in my darkroom sink and then very quickly and evenly sprayed the backside of the negative from about 12-16 inches away. One coat only. I think this may be the best solution to this problem if you have it. I don't like the idea of separate piece of mylar in my vacuum frame as it is one more thing to accumulate crud and dust. This way I can keep the glass pristine and concentrate on dusting the negative thoroughly.