Halftoning

[BetterSense]

I want to try making photo-etchings with infinite-contrast photoresist. To get continuous-tone results I think I will have to expose my continuous-tone negative onto the photoresist with some kind of halftoning process. I don't know where to start. Can I just hold a window-screen a few mm above the easel when I go to print? It seems to be a lithographic process I don't see discussed much. Has anyone tried to make printing plates from continuous-tone negatives? It would seem to be a similar process. Do I need a special screen?

[Jac@stafford.net]

May I ask why you want to use photoresist with its special lighting requirements rather than a high resolution film?

By 'infinite-contrast' you mean strictly black and white, correct? You can FAPP do that with available process films.

[smithdoor]

Halftone is use for printing It is done by High contrast Film/Developer and using a contact screen 30 years they had a halftone film that did not need a screen. Note photoshop has this Filter some have use just a screen from a window (I have never try this but looks good too) . I have use both contact screen and photoshop.

Dave


I want to try making photo-etchings with infinite-contrast photoresist. To get continuous-tone results I think I will have to expose my continuous-tone negative onto the photoresist with some kind of halftoning process. I don't know where to start. Can I just hold a window-screen a few mm above the easel when I go to print? It seems to be a lithographic process I don't see discussed much. Has anyone tried to make printing plates from continuous-tone negatives? It would seem to be a similar process. Do I need a special screen?

[BetterSense]

The photoresist will be applied to the substrate which is to be etched. It's a necessary element. However, it may make sense to generate a halftone image on litho film then contact-print that to the photoresist. How can I generate such a halftone negative?

[Jac@stafford.net]

The photoresist will be applied to the substrate which is to be etched. It's a necessary element.

Why photoresist? What can it accomplish that cannot be done with conventional methods?

[smithdoor]

Try looking at screen printing they still have to do it the old way. I use a Process/copying camera 25 years ago.
The easy way if the still make the film today I use photoshop.


The photoresist will be applied to the substrate which is to be etched. It's a necessary element. However, it may make sense to generate a halftone image on litho film then contact-print that to the photoresist. How can I generate such a halftone negative?

[BetterSense]

Photoresist is the conventional method. What other etching method is there (besides direct laser etching)?

[Jac@stafford.net]

Photoresist is the conventional method. What other etching method is there (besides direct laser etching)?

Conventional method for what other than electronics plates, making masks for further etching, counterfeiting (poorly) etc? More specifically, of what use it in large format photography? What kind of resolution do you wish to achieve? Dot (or other shaped) halftones are rather low quality. Stochastic halftones (AKA: FM) can support higher frequency/quality, however possibly not as high quality as you need or wish.

But before going further, it would be good to know what you wish to do so we don't waste time on the impossible or irrelevant.

[BetterSense]

I want to try making photo-etchings with infinite-contrast photoresist. To get continuous-tone results I think I will have to expose my continuous-tone negative onto the photoresist with some kind of halftoning process. I don't know where to start

I don't know anything about halftone processes so I cannot give a step by step description of "what I want to do" or I wouldn't need help in the first place. Perhaps it was a waste of time asking for help, and I shall just go re-invent halftoning (poorly) by myself. Or, somebody could direct me to some resources relevant to the practicalities of making halftone reproductions; that would be swell.

[Jac@stafford.net]

Just like etching PC boards, only I want to approximate a continuous-tone image, and as you know, photoresists are not a continuous-tone medium. I don't know anything about halftone processes so I cannot give a step by step description of "what I want to do" or I wouldn't need help in the first place. Perhaps it was a waste of time asking for help, and I shall just go re-invent halftoning (poorly) by myself.

My favorite, perhaps dated source is Dan Burkholder's information on making digital negatives. He has a great explanation of how halftones of various kinds are made both traditionally and digitally. Begin here. (http://www.danburkholder.com/Pages/main_pages/Digital_Neg_Info/Digital_Negatives.html) I do not know if making a digital negative can transfer seamlessly into etching a plate (gravure process.) Lithography might be better. Good luck. Remember: Stochastic halftones.

[mdarnton]

Probably the easiest way to do what you want to do is to make your halftone on the computer from a scanned neg, as smithdoor suggests, then print out an enlarged neg on inkjet transparency film and use that to contact print on your photoresist material. A window screen is much too coarse for this--halftone screens were on the order of 150 (low newspaper resolution) to twice that or more for books.

I don't know what you're expecting, but probably getting the high end of that will be a losing battle, and you'll be lucky to make the low end work right. I messed with halftone offset printing in the 70s, and it was real twitchy. I took a class, and that helped. There was a lot to know, and I don't know where you'd get that info these days. Your best bet is to find someone who's actually doing it, today.

[Nathan Potter]

I assume you are considering a UV sensitive photoresist similar to that once made by Shipley Corp. or other suppliers. Not quite infinite contrast but very high contrast and typically spin coated on plates to thicknesses in the range of 0.5 to 10 µm. You need to make sure the resist is compatible with the etchant to be used. Sometimes it is wise to use an adhesion promoter under the resist to avoid premature lifting of the resist mask.

Yes, you need a photomechanical dot original as a contact exposure mask for the photoresist. It must be in contact mode in order to resolve the dot pattern completely and accurately. For fine dot patterns vacuum contact is almost a must.

I used to use Kodalith Ortho film to generate the dot mask by contact exposing the continuous tone original to the Kodalith through a standard dot mask. You can buy dot masks at different dot sizes and pitches depending on the quality of the final image you desire. There are current equivalents to the Kodalith Ortho photomechanical film available from Freestyle Photo.

It may be possible to generate a dot master of the original continuous tone image using only Photoshop then output that dot image to a clear film like Pictorico as long as you don't use a very fine dot pitch. I'm not adept at such PS practice - others here may be.

I may be able to give you more guidance on the photoresist intricacies if I knew more about the material to be etched, the type of resist (novolak resin?) etc.

Nate Potter, Austin TX, Holliston MA.

[BetterSense]

The resist is standard fare photoresist (SPR3622 or similar) and I plan to experiment with materials.

I have Freestyle Arista Ortho Litho film, but I have been told that when using it for this purpose that one is supposed to use a special developer. Is that true or will Dektol work?

Contact printing through a dot screen sounds easy enough but where to get the dot screens?

[Andrew O'Neill]

I was formally trained as a printmaker, back in the 80's. Lithography and intaglio. All my halftones were made by a blueprinting company, downtown Victoria. It's just an art store now. Your best bet would be to just make them in PS, and print out on Pictorico or something similar.
Here is an example of halftone image I whipped up in a matter of minutes. If I were doing intaglio today, I'd contact print it onto a plate that had been treated with ammonium dichromate sensitized gelatine, and expose under a UV source. Areas that receive UV will harden. Areas that do not will wash away in a warm water bath. Slide the plate in the acid bath and etch.

[Nathan Potter]

OK, a bit more information. I'm not familiar with SPR3622 but if std. fare then it is likely a positive acting novolak resin with azo sensitizer.

Arista Ortho Litho film should work but only with a high contrast litho developer. Aristo should be able to supply such.

Try Edmund Scientific for dot screens. You'll obviously need a screen to match the film size of the continuous tone original.

I'm not at home now so don't have access to my old notebooks but I've done what you want to do some years ago so I'll try to summarize.

1. Grab your continuous tone original B&W negative.
2. Place the unexposed litho emulsion side up on the bottom. Place the dot mask on top of the litho film
emulsion side down. Place the continuous tone film emulsion side down on top of the dot mask.
3. Expose the B&W original thru the dot mask and onto the litho film. The exposure time is critical - you'll need
to experiment with exposure and development times.
4. Develop the lith film in lith developer for a time necessary to yield a dot pattern where the size of the dots is
approximately linear with the density of the B&W original. (The low density areas of the original over expose
the lith film thru the dots causing the dots in silver on the lith film to expand such that in this reversal
process highlight areas of the original create larger dots of silver representing highlight areas in the litho
film).
5. Now since I believe you have a positive acting photoresist and you now have a negative acting lith you will
need to produce a copy of the negative lith film by contact printing onto another piece of lith film. For this use
the lith developer again but with exposure and development times that will not change the dimentions of the
dot pattern.
6. Using the second generation lith film with the integral dot pattern you next contact print that positive image
onto the positive acting photoresist pattern. Note some caveats in this part of the process. The litho film dot
density must be high enough to avoid any significant print thru the opaque areas. Dust is a major headache
with photomechanical film processes so try to be dust free as much as possible depending on your tolerance
for such defects. If you use a fine dot pattern then vacuum clamping of original to photoresist is adviseable.
7. Expose the photoresist thru the lith dot mask typically with UV light depending on the sensitizing region of the
resist (typically 365 nm mercury line for azo sensitized novolak resin). Develop the resist image (typically a
solution of sodium hydroxide or equivalent). Again you'll need to work out the exposure and development
times (not trivial).

It can be common with some metals to use an adhesion promoter (HMDS, Hexamethyldisilazane) to enable better adhesion of resist to metal, especially with copper, aluminum. Not so with titanium and chromium.

Hope this is a bit of help.

Nate Potter, Austin TX., Holliston MA.

[marfa boomboom tx]

Search for aquatint screen...

[invisibleflash]

OP, that stuff is all dead. Digital killed it.

Back in the 70's we used glass or film halftone screens with the process camera. The glass screens were above the camera and rolled down. (I let one fly by accident and the screen got cracked. ) Film screens had to be used with a vacuum back or it took on a moire.

http://graphicdesign.spokanefalls.edu/tutorials/tech/halftones/images/copycamera.gif

I'd keep an eyey out on ebay if any screens come up. If you want sharp dots go with litho film and litho developer.

[smithdoor]

I have made halftones back to 70's Today if I need one I just use photoshop there are others I use before I had photoshop they all work great.
Note Kodak made a lot of contact screens for halftone work
I also made my process camera

Dave



OP, that stuff is all dead. Digital killed it.

Back in the 70's we used glass or film halftone screens with the process camera. The glass screens were above the camera and rolled down. (I let one fly by accident and the screen got cracked. ) Film screens had to be used with a vacuum back or it took on a moire.

http://graphicdesign.spokanefalls.edu/tutorials/tech/halftones/images/copycamera.gif

I'd keep an eyey out on ebay if any screens come up. If you want sharp dots go with litho film and litho developer.

[Gary Beasley]

If indeed you can find all the parts to produce a halftone don't confuse a tone screen with a true halftone screen. Tone screens are used to produce a tint in a percentage of area covered, as in a 10% screen makes a light tone and a 50% screen makes a dark tone. You can tell the difference by examining the screen under a loupe, the halftone screen has fuzzy edged dots and the tone screen will have sharp edged dots [not talking of the classic glass screens but the plastic one that take a vacuum]. You can use a tone screen on a photograph but you will merely get posterised images in that tint range instead of a true halftone representation of the image.

[marfa boomboom tx]

If indeed you can find all the parts to produce a halftone don't confuse a tone screen with a true halftone screen. Tone screens are used to produce a tint in a percentage of area covered, as in a 10% screen makes a light tone and a 50% screen makes a dark tone. You can tell the difference by examining the screen under a loupe, the halftone screen has fuzzy edged dots and the tone screen will have sharp edged dots [not talking of the classic glass screens but the plastic one that take a vacuum]. You can use a tone screen on a photograph but you will merely get posterised images in that tint range instead of a true halftone representation of the image.


search: kodak magenta half-tone screen --- that's what this was…

[smithdoor]

If you looking for a real screen try here
http://www.caprockdev.com/camera.htm

Good luck
Dave

[BetterSense]

Sometimes I wish I was living in about 1975. That's late enough to benefit from LPs, transistors and urethane skateboard wheels, but early enough to avoid Microsoft, ABS and the TSA.

I simply don't have the computer hardware for photoshop and I don't want to start down that road. I will try to dig up a halftone screen and maybe do some experimentation.

Based on the descriptions of the technique, it sounds like I may be able to sandwich a halftone screen with a resist-coated substrate and expose it in-camera. It will be flipped and negative, but the final etching may end up appearing positive.

Photoresist will always be available because it's used for electronics manufacture. I'm not aware of it being used for pictorial purposes, for obvious reasons of its spectral sensitivity and contrast.

[Bill Burk]

The first halftone screens were ruled black parallel ink lines on two thin sheets of glass, and then assembled at right angles face to face .... These were held slightly above the film so it cast a shadow of fuzzy white spots.

A Contact Screen is an out-of-focus picture of the same thing.

The fuzzy spots work like a pattern of grayscales, the center is the first to become exposed and will make a tiny black spot with less light, while a dot that gets more light will spread out and become a bigger black spot.

It's funny that now it's harder to come by these screens, and it would be pretty easy to make halftones by computer with a Raster Image Processor.

[smithdoor]

Try a old print shop or craigslist they may have one to give to you
FYI I did to big deal same as today but I had money

Dave


Sometimes I wish I was living in about 1975. That's late enough to benefit from LPs, transistors and urethane skateboard wheels, but early enough to avoid Microsoft, ABS and the TSA.

I simply don't have the computer hardware for photoshop and I don't want to start down that road. I will try to dig up a halftone screen and maybe do some experimentation.

Based on the descriptions of the technique, it sounds like I may be able to sandwich a halftone screen with a resist-coated substrate and expose it in-camera. It will be flipped and negative, but the final etching may end up appearing positive.

Photoresist will always be available because it's used for electronics manufacture. I'm not aware of it being used for pictorial purposes, for obvious reasons of its spectral sensitivity and contrast.

[smithdoor]

Try this film just found it looking for other film
http://www.ultrafineonline.com/10x12100utpr.html

Dave

[Gary Beasley]

Now on top of needing all the components you will need to know how to use the halftone screen. There's more to it than just exposing an image through the screen and processing it. First you will need to determine your "bump" exposure to create the shadow dots, this is a non image exposure with the screen on to bring up the exposure threshold of your material to the point that any more exposure results in a definite dot in the image. Then you need to determine your highlight exposure on top of that, which is what you need to create a small dot in the highlight area that is not closed up or greyed over. This is complicated by changes in the developing time affecting the size of the dot. In actual practice a close approximation of the exposure is found and fine tuned with the development by inspection if tray developing. Machine or timed processing allows you fine tune by exposure alone.
The magenta screen can also be manipulated with filters to change the contrast response, which is why most cameramen making a halftone of color prints liked a grey screen. You also have a choice between elliptical dot and square dot. An elliptical dot screen had a smoother midtone gradation as the dots are slightly elongated to the diagonal so the dots connect at two opposite corners then the other two with a little more exposure. A square dot joins at all four corners at once and can look more contrasty in the midtones.