Newton, NuArc and OHP

[SusanV]

Hi,

When I use OHP sheets in my Nuarc, there are tons of little Newton's rings-looking things that develop between the glass and OHP as the vacuum pulls it all together. I know a lot of you use Nuarcs and OHP... is this a common occurance, and does it cause irregularities in the exposure? I've tried different pulldown time, and amounts of vacuum from 5 to 22 "hg, and they're still there... they just get smaller but more numerous with more vacuum.

I don't actually think they're causing irregularities for my polymer plate exposures, but if there's a way to eliminate them, I'd love to know.

thanks,
Susan

 

[Michael Mutmansky]

Susan,

Anti-newton spray... I've heard that some people use hairspray to the same effect, but I haven't used that.

I don't know whether any of these sprays might have UV blocking properties. I suspect not, but you'll probably want to test for that.

I can tell you that with dichromated colloids, the newton rings will show up, but I don't know whether the solarplate will have a similar problem.


---Michael

 

[Joe Lipka]

I have a NuArc 1722, I have not had this problem with Newton rings.

 

[SusanV]

See, that's what has me puzzled. Why would OHP, vacuum pressed against glass react any differently for you than me? It happens at 5" or 22"hg, so the pressure isn't the issue, but I'd sure like to know what is. I'm using a NuArc 26-1K... does the type of glass make any difference? My unit was used when I got it... maybe the glass has been replaced by an inferior type?

I have a flexible rubber bed that lifts up against the glass during drawdown. it has the grooved surface to allow airflow.

So what's making the difference? Any ideas on this appreciated.

susan

I have a NuArc 1722, I have not had this problem with Newton rings.

 

[SusanV]

Hi Michael... Yeah Krylon has some sprays that have minimal UV block (#1303 clear spray for instance). That might be a help.

I just wish I could figure out why some people get the rings and some don't. I mean, if it's just a matter of me standing on one foot while I turn on the vacuum, I can do that

Susan

Susan,

Anti-newton spray... I've heard that some people use hairspray to the same effect, but I haven't used that.

I don't know whether any of these sprays might have UV blocking properties. I suspect not, but you'll probably want to test for that.

I can tell you that with dichromated colloids, the newton rings will show up, but I don't know whether the solarplate will have a similar problem.


---Michael

 

[Michael Mutmansky]

I have a NuArc 1722, I have not had this problem with Newton rings.

Unless you take measures, there are newton rings present, even with normal film. Pt/Pd doesn't seem to mind them at all, however. Neither does gum in my experience. But I have heard from a copper gravure printer that the newton rings with OHP are visible.

That's essentially carbon printing, but this guy works at a level far above most people, so what is an acceptable level of performance for most people won't be for him.

---Michael

 

[SusanV]

Thanks Michael, that seems very clear then... I need to get rid of them. I'm first of all a printmaker, so it's important for me to get the cleanest tone possible. I've had little irregularities that come and go, but I've been learning to control them once my plate is etched, through my inking and wiping technique. Now I'll check into anti-newton sprays and such, and work on eliminating them.

Susan

Unless you take measures, there are newton rings present, even with normal film. Pt/Pd doesn't seem to mind them at all, however. Neither does gum in my experience. But I have heard from a copper gravure printer that the newton rings with OHP are visible.

That's essentially carbon printing, but this guy works at a level far above most people, so what is an acceptable level of performance for most people won't be for him.

---Michael

 

[sanking]

Hi Michael... Yeah Krylon has some sprays that have minimal UV block (#1303 clear spray for instance). That might be a help.

I just wish I could figure out why some people get the rings and some don't. I mean, if it's just a matter of me standing on one foot while I turn on the vacuum, I can do that

Susan

Susan,

I have used the NuArce 26-1k and now a similar light, the AmerGraph ULF-28, and have not experienced Newton rings with kallitype or pt./pd. However, I have seen a strange kind of mottling with carbon printing that others have observed as well. It is very strange because you only see it area of the print with broad areas of even tone at about the equivalent of Zone VI.

In additon to the anti-newton ring spray, another solution is to dust over your negative with talcum powder. It is not nearly as messy as it sounds.



Sandy King

 

[Joe Lipka]

Michael does have a good point. Paper texture does have the wonderful ability to hide negative flaws that would show up on a smooth texture paper. I use COT 320 as a standard printing paper. I will be testing some of the Weston paper later on this year, so we'll see if that makes a difference.

 

[Michael Mutmansky]

Sandy,

That sounds suspiciously like the problem the gravure printer was describing to me. Try AN spray or hairspray, and see if it disappears. You should be able to see an improvement on the treated film when sandwiched in the vacuum frame. If there isn't a visible improvement, then you will need to try a different AN method...

It could be related to differences in pressure caused by paper thickness variations, or any number of other things I suppose, but in this case, it's easy enough to test and eliminate the variable to see if newton rings might be the source.

I think some of these films have an inherent problem that they are more prone to newton rings. They seem to have a birefringence effect that is stronger than film, and it could be interacting with the newton ring effect to increase the strength of the optical effect.


---Michael

 

[sanking]

Sandy,

That sounds suspiciously like the problem the gravure printer was describing to me. Try AN spray or hairspray, and see if it disappears. You should be able to see an improvement on the treated film when sandwiched in the vacuum frame. If there isn't a visible improvement, then you will need to try a different AN method...

It could be related to differences in pressure caused by paper thickness variations, or any number of other things I suppose, but in this case, it's easy enough to test and eliminate the variable to see if newton rings might be the source.

I think some of these films have an inherent problem that they are more prone to newton rings. They seem to have a birefringence effect that is stronger than film, and it could be interacting with the newton ring effect to increase the strength of the optical effect.


---Michael

Michael,

The same thought passed through my head me when you mentioned the problem of the gravure worker. There was a disussion of this not long ago on a carbon forum and the commerical carbon/gum prnting team from Sweeden, Hans and Chia, mentioned that they had also had similar problem, and had given up using the vacuum for carbon, which resolved the issue. I surely don't want to do that, however, because there is a real difference to my eye in sharpness in a carbon print printed with and without vacuum pressue. It never crossed my mind that it might be a problem related to Newton rings. Definitely worth tying some anti-newton fix.

Nothing about this that I have seen in any of the literature on carbon or gravure.

Sandy

 

[bobherbst]

Newton Rings

Newton rings show up any time you have the shiny mylar side of the film pressed against glass or even another piece of film. I've seen them in scanners when scanning film, contact printing frames, vacuum tables of various brands including the Nuarc 26-1K and my Douthitt vacuum table. I clean the glass of my vacuum frame for every printing session and they are still always there. You will even see them between two sheets of OHP which is how I teach students to check if they have only one sheet pulled out of the pack. It is the result of refraction of the light across the air interface between the two materials and is usually enhanced by higher humidity conditions. The only place I have had the rings actually show up in a print was when contact printing 8x10 negatives onto glossy silver gelatin paper in a contact or vacuum frame. I have never seen them show up in a Pt/Pd print and I've made many thousands in a variety of contact frames and vacuum frames. Unless you are seeing them in the print, don't worry about them. I have a general aversion to spraying or dusting ANYTHING onto my negatives.

Bob

 

[SusanV]

Sandy... yes, a smooth area of tone from about zone 5 and up will show it with gravures. The gravure plate has a very smooth surface that will pick up any irregularity, but the deeper tones of the plate wash away to varying degrees during development, and I assume, take the mottling with them.

As for talcum... we gravure folks have been doing that already.... but between the OHP and the plate, which have a too-strong attraction for each other, and cause a different kind of mottling with larger areas of light blotches. Now I'll add the powder to the top of the film as well.

There is another way of going about this, since I am now convinced I understand the cause of my problem (thanks all of you)... There is a material that can be fitted to the vacuum table in place of glass. Jon Lybrook uses it with good results, and I even bought a piece of it but haven't done the modification yet... maybe now I will. It is called Kreene, and is a vinyl-type of thin, translucent material. If anyone is interested, it can be purchased from Boxcar Press, online. I'll try to get it set up on my Nuarc and try it, and report back here for those interested.

thanks a lot,
Susan

Susan,

I have used the NuArce 26-1k and now a similar light, the AmerGraph ULF-28, and have not experienced Newton rings with kallitype or pt./pd. However, I have seen a strange kind of mottling with carbon printing that others have observed as well. It is very strange because you only see it area of the print with broad areas of even tone at about the equivalent of Zone VI.

In additon to the anti-newton ring spray, another solution is to dust over your negative with talcum powder. It is not nearly as messy as it sounds.



Sandy King

 

[sanking]

Sandy... yes, a smooth area of tone from about zone 5 and up will show it with gravures. The gravure plate has a very smooth surface that will pick up any irregularity, but the deeper tones of the plate wash away to varying degrees during development, and I assume, take the mottling with them.

As for talcum... we gravure folks have been doing that already.... but between the OHP and the plate, which have a too-strong attraction for each other, and cause a different kind of mottling with larger areas of light blotches. Now I'll add the powder to the top of the film as well.

There is another way of going about this, since I am now convinced I understand the cause of my problem (thanks all of you)... There is a material that can be fitted to the vacuum table in place of glass. Jon Lybrook uses it with good results, and I even bought a piece of it but haven't done the modification yet... maybe now I will. It is called Kreene, and is a vinyl-type of thin, translucent material. If anyone is interested, it can be purchased from Boxcar Press, online. I'll try to get it set up on my Nuarc and try it, and report back here for those interested.

thanks a lot,
Susan

Susan,

Do you mean that the Kreene is used in place of the glass, or is it attached to the glass?

I had been theorizing on ways to pemanently solve the problem and had though of spraying anti-newton on the inside of the glass iteself. Or of using some type of very thin and clear vellum between the negative and the glass.

Sandy

 

[SusanV]

Sandy,

The Kreene is used instead of the glass. It's suspended across a frame that holds it down against the raised edge of the vacuum bed, then the vacuum pulls it down. Jon Lybrook from the alt list uses it and swears by it.

I've also been thinking about some vellum or other material between the glass and the film (ohp). I wonder if a piece of kitchen plastic wrap would do... wouldn't THAT be a sweet and simple solution. ha.

Another thing I experimented with a little... I made a cut-out window in a piece of foamcore, and placed my plate/ohp sandwich in that during exposure. I'd also placed a stiff base under it so the flex bed couldn't move upward. The sandwich was never pressed against the glass... it was just held together by the vacuum eliminating the air between the layers. I had some success with that, but then ran into some other problems with the process in general, and that trial kind of got left by the wayside as I turned to solving other problems... now I've gotten most of this thing figured out, and I'm returning to some of these early issues.

Susan

Susan,

Do you mean that the Kreene is used in place of the glass, or is it attached to the glass?

I had been theorizing on ways to pemanently solve the problem and had though of spraying anti-newton on the inside of the glass iteself. Or of using some type of very thin and clear vellum between the negative and the glass.

Sandy

 

[SusanV]

Bob,

Yes the idea of dusting talc on my negatives... actually we use positives for this process, went totally against all I've ever believed, but it's not the end of the world, as I've found out. It's an absolute necessity when exposing polymer plates sandwiched with OHP, for making photogravures. The surface of the polymer plate grabs the ohp and traps air otherwise. So... we already dust talc between the ohp and plate... adding another dusting between the glass and ohp could be a solution for this. Understand that almost all the talc is gently brushed off, leaving almost no visable sign it's there.

And yes, the newton's rings do leave their mark on my plates and they show up in the print. They have GOT to go :eek:

susan

I have never seen them show up in a Pt/Pd print and I've made many thousands in a variety of contact frames and vacuum frames. Unless you are seeing them in the print, don't worry about them. I have a general aversion to spraying or dusting ANYTHING onto my negatives.

Bob

 

[MVNelson]

I have a new to me, used NuArc VFC43 and noticed the glass/film interface you describe also...the higher the pressure the finer the ring pattern...didn't show up on pt/pd prints...however, offset printer's powder resolved the issue... I got some years ago from a service bureau... a free scoop (last for ever)...

Miles

 

[sanking]

I have never seen them show up in a Pt/Pd print and I've made many thousands in a variety of contact frames and vacuum frames. Unless you are seeing them in the print, don't worry about them. I have a general aversion to spraying or dusting ANYTHING onto my negatives.

Bob

Talc is an inert substance that should not do any damage to your negatives. It has been widely used in the graphic arts industry for decades.

I think it is quite safe even with valuable in-camera negatives. In this thread we are talking about digital negatives , which can be reprinted if necessary.

Sandy

 

[SusanV]

Glad Cling wrap vs Newton's rings

Hi all,

I don't yet have the time for a full test of this idea, but I was just too curious... so I smoothed a piece of Glad Cling Wrap to the top of a piece of pictorico ohp, put it in the Nuarc and pulled a vacuum. NO Newton's rings visable at all. None!

it was a little hard getting it smooth, but the idea is definitwly worth visiting further. Different brands, application with a brayer maybe, etc... In fact as I think out loud here... maybe some type of film sqeegeed onto the inside of the glass itself...

ok so the wheels are turning on this... brainstorming from interested parties welcomed!

I might be able to get into the studio tonight and do a proper exposure, print etc., I'll report back.

Susan

 

[Michael Mutmansky]

Susan,

It is possible to get single and double sided mylar that has a tooth to it. It will be much thicker and not prone to wrinkling compared to regular wrap, and it may make a suitable overlayment. I think I have some here, so I may play with it the next time I'm in the darkroom.

I'll bet there are lots of materials that could be made to work, all it takes is some time to try them all.

---Michael

 

[Jeremy]

I don't yet have the time for a full test of this idea, but I was just too curious... so I smoothed a piece of Glad Cling Wrap to the top of a piece of pictorico ohp, put it in the Nuarc and pulled a vacuum. NO Newton's rings visable at all. None!

maybe some type of film sqeegeed onto the inside of the glass itself...

I'm going to try taping the glad to the underside of my glass and seeing if that will work.

 

[sanking]

Just to see what would happen I sprayed a sheet of thin (3mil) mylar with a coat of satin finish polyurethane. I placed this between the OHP and glass of my ULF-28 and turned on the vacuum and light. It visually eliminated all signs of the newton rings that would have otherwise been present. I tested with carbon using the negative that was giving me trouble and did not see the mottling. No guarantee, however, since I am not seeing the mottling 100% of the time anyway.



Sandy King

 

[Jeremy]

I had a negative I didn't flip horizontally when making the digital negative so I decided what the hell! and tossed it into the NuArc. The outside edges where there is no ink shows the mottling, but zero mottling in the negative.

The inked side of the OHP is pressing against the glass.

I'm wondering if I'll get sharper prints from 8psi through the substrate or in a contact frame with the ink against coated paper....

 

[clay]

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.

 

[sanking]

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

Is this Pictorico?

Sandy