Polymer Gravure

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ImagOn Screened

Posted by on 11 Jun 2009 | Tagged as: Polymer Gravure

When kicking around ideas of different uses for ImagOn polymer film we decided to try it at printing photographs that were screened in Photoshop. You can find info on this topic and the vast possibilities of ImagOn in Keith Howard‘s books Non-toxic Intaglio Printmaking and The Contemporary Printmaker: Intaglio-Type & Acrylic Resist Etching.

Here we have a quick experiment; we first created a tone compensation curve, and then applied it to any grayscale image to be screened and converted to bitmat mode for outputting to an inkjet printer.

An ImagOn test print and a plate. Note the open bite that occurs at the darkest tones – the screen frequency is too high, or the printer is outputting too much ink (for this purpose) so the light cannot pass during the exposure.

The curve can be created for halftone screened images as well as for continuous tones (again ChartThrob does a good job here), but when using ImagOn and inkjet technique we tend to clip the tones somewhat, especially at the dark end of the range.

Our curve for Andromeda’s EtchTone screen at 85 lpi frequency. The curve is very straight, it is messed up by open bite at the darkest tones. Actually the curve we finally used was adjusted by just straightening it to the left edge (the gray line).

Besides Photoshop’s own (actually quite good) dithering methods there are other software tools for screening images. Some of them work as Photoshop plug-ins, accessible from the filter menu, for instance.

Enlarged portion of a bitmap image showing the EtchTone’s SteelEtch screen.

Depending on the chosen screening technique, the outcome can be finely dotted screen, almost invisible to the naked eye, or coarse special effect, breaking the image surface down to larger dots. We tried Andromeda Software‘s EtchTone plug-in (among others), finding it quite interesting but hard to control – with the inkjet technique and our line frequencies we couldn’t get rid of posterization, which showed annoyingly especially on some tone gradients.

An ImagOn print from a plate exposed through a screen film positive. Notice the heavy posterization in the sky area.

We are done with testing ImagOn and other polymer plates for now – some of the students are experimenting on their own – maybe we will hear from them some day…


Posted by on 24 May 2009 | Tagged as: Polymer Gravure

Polymer plates like Toyobo or Solarplate are expensive, but there is much cheaper polymer material, called ImagOn, that can produce much the same look.

ImagOn is light sensitive polymer film, sold in rolls. The film can be laminated (commonly with water) on many types of base materials (copper, zinc, aluminium, plexiglass) and then used like other polymer plates. The film is very thin compared to polymer plates – a reason why its ability to form grooves deep enough for holding the printing ink (needed to render the darkest tones) has been sometimes questioned.

We laminate ImagOn film on aluminium offset plates. The plates come disposed from a printing house, but after cleaning they are perfect for carrying the ImagOn film. There is a top Mylar protective layer on ImagOn, it can be left on or ripped off before the exposure – the resulting image will vary by contrast and tone scale depending on which choice was used.

The blue ImagOn film can be laminated on many materials – we have been using aluminium plates, which can be easily cut to different sizes after lamination.

A laminated ImagOn plate can be handled and exposed the same way as the thicker polymer plate, but it seems to be much more sensitive to UV, needing shorter exposures. It is developed in 1% sodium carbonate solution for 2 minutes, with the top layer removed.

We started testing the material with our system, finding first a decent exposure for the screen (we were using the same aquatint screen as previously for the Toyobo plate). Our most promising screen exposures were around 10 seconds.

An aquatint screen exposure test. At 5 seconds exposure the plate is under exposed and shows an area of open bite (ink will not hold there), 10 seconds looks pretty good, and 15 seconds and more are overexposed (no black any more).

Next we made a test print where a 101-step tablet was exposed on the plate after the screen exposure. Both exposures were 10 seconds, with the top Mylar left on. After processing the plate we noticed that the exposure for the stepwedge could have been even shorter in order to shift the tones higher, towards highlights (a positive process: less exposure darkens the image). But it is a pain to get constant repeatable exposures shorter than 10 secs with our uv unit, so we decided to continue with these exposures. The important thing is to be able to find both maximum black and paper white from the test strip, so that the curve can be constructed.

A screen exposure and 101-step wedge exposed on ImagOn, both exposures 10 seconds. After processing and printing the plate (left) the tone compensating curve was derived.

After a number of test prints we came to conclusion that it’s not easy (for us anyway) to pull prints from ImagOn with good photographic tonality. Besides, we had a very busy study module with students on this topic, with so little time for printing…

Saara Leppäkoski: ImagOn Gravure.

The next thing to try will be exposing ImagOn through screened films, with no separate screen exposure … actually done that already – but more later…

Polymer Gravure

Posted by on 18 May 2009 | Tagged as: Polymer Gravure

We have now constructed some correction curves for polymer gravure. Before calculating the curve shapes we have worked out our standard exposure times for polymer plates. After applying the curves the image files were printed (as positives) on transparency film. Here we were using an Epson 1800 with all inks, there was no need for finding the best UV-blocking colors here, as we don’t need such high densities for polymer.

Our polymer curves: The first one created by ChartThrob, the second one corrected by hand to reduce posterization of print shadow tones.

Our polymer plate is Toyobo Printight, exposed with UV light first through a fine aquatint screen and then through the positive transparency. Both exposures have to be done with perfect contact between the film and plate, we use a vacuum frame for this. We acquire top quality aquatint screens from Kari Holopainen, a pioneer in polymer gravure in Finland.

After the two separate exposures the plate is developed or “etched” by washing in water, dried, and hardened with another exposure to UV light.

A processed polymer plate. (This plate was pulled through a press once – there is still some ink left in the darkest shadows…)

The plate is then inked with intaglio ink, wiped and printed with an etching press just like any other intaglio plate.

The first print from the plate above. The tone correction curve that was applied to the image file is working satisfactorily, and it can be further corrected, as needed, to match better special type of images.

Next some of our students’ work. Their workflow in polymer gravure is mainly based on these excellent sources:

Polymer Photogravure by Taneli Eskola and Kari Holopainen (or actually its Finnish edition).
Jon Lybrook‘s site Polymer Photogravure for More Photographic Intaglio Prints.

Saara Leppäkoski: Polymer Gravure.

Saara Leppäkoski: Polymer Gravure.

Hanna-Kaisa Kuronen: You Keep Me Sane, Polymer Gravure.

Our polymer gravure process outline:

1. A digital grayscale file is created from the original image. In Photoshop, a correction curve (created by ChartThrob script) is applied. The file is then printed on transparency film as a positive.
2. A polymer plate is cut to the film size. The protective film on top of the plate is removed (in dimmed lightning).
3. The plate is exposed to UV light in contact with an aquatint screen, then with the positive transparency. Our exposures are 80 seconds for the screen plus 80 seconds for the film, but these can vary greatly depending on equipment used – testing is recommended.
4. The plate is then developed by immersing in water and gently scrubbing with hand or sponge. More exposed areas of the plate have been hardened, while less exposed parts will be washed away, leaving “holes” to keep printing ink later. We wash the plates for about 2 minutes in cool water (room temperature).
5. The plate is blotted dry, and an extra uv exposure (ca. 5 minutes) is given (without any films) to harden it for printing.
6. We have basically an etching plate now, ready to be intaglio printed. We will now ink the plate, and while we wipe off extra ink to clean the highlights, the ink will remain in the grooves and produce rich deep shadow tones.
7. An etching paper is dampened and pulled in contact with the plate through an etching press. The paper picks up the ink from the plate and forms the gravure print.

Polymer Probing

Posted by on 02 May 2009 | Tagged as: Polymer Gravure

A polymer plate, films and prints from my “standard test image”.

During the past couple of weeks our students have been experimenting with photopolymer gravure. We’ve been using Toyobo Printight polymer plates and ImagOn polymer film.

We will report back on our results soon – all we can say right now is we have a feeling for thicker Toyobo plates being better in photographic continuous tone work, while ImagOn film can be just great for line art and screened images…