Photopolymer intaglio printing with DK3 film
Notes on making photopolymer intaglio prints with DK3 film
I've been making 'alternative process' prints for a while now, including cyanotypes, Van Dyke Brown, carbon transfer and gum bichromates. While some of these processes have yielded results I like a lot, I can't really settle on one single process. One night, wondering about lithography (quite randomly), I watched some videos on lithographic printing. I liked what I saw, so I did some more research into the process. I quite quickly decided that it wasn't very feasible in a home setting, requiring an offset press, plates and all the materials and skills to make this wonderful but complex process work. But I continued reading and stumbled onto the process of intaglio printing, and particularly photogravure. The process somehow appealed to me, as did the results others were achieving, so I bit into the subject.
I quickly found out that the currently fashionable approach is to use photopolymer instead of a copper or zinc plates, making the process somewhat more doable in a home setting. The only really expensive bit of equipment needed was an etching press, and within a few weeks I found one - *gasp* at the price, even second hand, but bit the bullet anyway. Materials, including photopolymer and etching inks and papers, were ordered and within two weeks, I was making intaglio prints. No exhibition-quality results yet, but a lot of fun (and the inevitable frustration) and just enough of a result to keep at it for a while. In this article, I'll share my working methods, but I'll also document the issues I've run into and the solutions I've come up with. It's a work in progress, so the information is somewhat preliminary and should be taken with a grain of salt, but hopefully it'll be helpful to someone.
I could write a lengthy essay on the history and details of the process, but many have done so - and probably better than I could do it. I'd recommend looking for online and offline sources for general overviews. I'll share a few pages that I found particularly helpful:
- Photopolymer printing on a budget - A good first step into the terrain of photopolymer printing, with some baseline parameters that seem to match my experience quite well.
- Polymetaal - A Dutch company specializing in the retailing of materials and equipment for printing processes, including all the materials needed for photopolymer intaglio printing. They also have some articles (if you search a bit; many are hard to find) that may be useful.
- Michael J Hopcroft's blog - A collection of blog posts detailing the search of a photographer for presentable photopolymer intaglio prints. He uses an Epson 3880 to produce the transparency positives and has documented some of the problems he's run into with using that particular printer. As I'm using the same printer, I found his detailed posts very useful.
- Sander Kunstdruck - Another series of articles written by a German artist on making intaglio prints with digitally fashioned positives. In German, but 'sehr gründlich': very detailed and (I found) reliable information on the entire workflow.
I have documented my (preliminary) workflow in a series of Youtube videos which can be found here:
As it's a work in progress, I have by now changed my methods a bit to counter some problems I ran into. Currently, I am working with the following parameters:
- A digital file is prepared with a contrast-reducing S-curve and the black point limited to about 76% to prevent open biting. I've tested with anything between 60% and 100% and found that 93% black is the densest I could get away with using longer exposures, and down to about 70% for very short exposures. Due to the high contrast of DK3 photopolymer, the process is incredibly sensitive to even minute variations in exposure time. This means timing to the second is a necessity!
- I suspect it's best to make a digital file with at least twice the resolution at which it's printed to prevent interference between the dither patterns of the digital file and the printer driver/Quad Tone Rip (see below), resulting in unnecessary graininess or moire-like patterns.
- I print my positives at 1440dpi using the matte black ink of my Epson 3880. 720dpi results in a coarser dot pattern which should theoretically result in a deeper black, but I found that 1440dpi already enables a very rich black and creates slightly finer details - although the difference in terms of detail is minimal. This is not a process for making tack-sharp prints, at least not when using a face tanner/solarium light source and inkjet printed positives. Stepping up again to 2880dpi only results in the printer laying down more ink, so the response curve of the material is changed, but no more detail or deeper black can be achieved this way. 1440 dpi (specifically the 'super' setting and unidirectional printing in Quad Tone Rip) seems like the best compromise.
- The Epson driver doesn't enable printing with black ink only at higher than 720dpi, which is why I use Quad Tone Rip. I created an ink profile using the black channel only, with the maximum ink density set to 50 (default is 80, I think). An ordered dither pattern produces the best prints for me. These parameters will vary wildly depending on materials and working methods elsewhere in the process, so they can only be a starting point for experimentation by others.
- The high sensitivity of the DK3 film also means that the lighting in the room as shown in the videos above resulted in unpredictable lighter areas (essentially fogging of the material) in the prints. So I had to switch to working under red LED lights instead of white LEDs and fluorescents when laminating, exposing and processing the film.
- I tried the dry lamination method explained here instead of the wet lamination method explained in the videos above and I found that dry lamination is quicker and apparently at least as effective as wet lamination. I also suspect that the wet lamination method can result in minute variations of moisture content and film thickness (due to squeegeeing) across the film, which can result in density variations in the print - not good! This is conjecture on my part, but the process is finicky and wet lamination influences two more parameters (moisture content and film thickness) in a specific way and I find this undesirable. I was afraid that dry lamination would create horrible problems with wrinkling of the film and debris being stuck between the film and the plate, but with a little bit of an eye for dust and debris in my workplace, I found this not to be an issue. The laminated plates need to rest for a few hours (I usually wait >24 hours before exposing them), otherwise the adhesion particularly along the edges of the plates will be imperfect, damaging the edges of the plates during inking and printing, with small fragments of hardened photopolymer sticking all over the place and the edges of the plate (and therefore print) ending up very uneven.
- Even though I use very cheap PVC sheets to laminate the film on (they're perfectly adequate for small editions), I found I liked to recycle them. Reclaiming the sheets is a bit of a chore since the photopolymer film adheres really well to the plate. Soaking the plates for a few hours up to several days in a water bath with a spoonful of cleaning soda dissolved into it softens the film, allowing it to be scrubbed off eventually.
- I store laminated plates separately in newsprint envelopes (just fold the plate into a sheet of newsprint) and tucked into a cardboard envelope, which is stored in a drawer. The plates should be kept in the absolute dark.
- I use a Philips face tanner/solarium (the same I use for cyanotypes and other alt. processes) and have so far found it to be adequate, despite other sources stressing that only collimated point sources (e.g. metal halide) are fit for photopolymer intaglio. The problem with non-collimated, strip/field sources such as UV fluorescent tubes is that the light is not entirely unidirectional, spreading out underneath the ink dots of the positive. This reduces the sharpness of the dots and therefore of the intaglio pattern in the plate. However, I find that even with this light source, very small, sharp dots can be imaged onto DIY-laminated photopolymer film plates (I'm not sure about the much thicker solar plates!) The light source, however, is one of the parameters I'm likely to address at some point in the future to optimize print quality. If you start from scratch, go for a point source such as the Osram Vitalux 300W UV bulb that is also promoted by Grafisk Eksperimentarium, the people who also market the DK3 photopolymer film that I use. The drawback of such a metal halide light source is twofold, though: they need a few minutes to warm up before the light level is stable and exposures can be made reliably and consistently (and they need to cool down for a few minutes if you want to switch them off and back on again), and they generate a lot of waste heat. Therefore, I find it desirable to work out a process that can be used with the much less cumbersome and efficient UV tubes. I know several people have produced satisfying results with them in combination with photopolymer film, so it seems to be a matter of dialing the correct process parameters.
- To prevent newton rings (creating light/dark spots in the print), I gently dust the smooth side of the transparencies with talcum powder. I'm not sure if this really helps, but it doesn't seem to hurt either. The printed side of the transparencies I use (see my videos for the brand and type) has a nice, sticky tooth to it, so it's unlikely to produce newton rings.
- The optimum exposure time I arrived at with the mentioned face tanner (4x15W UV tanning tubes) at a distance of about 36cm from the printing frame is about 25-30 seconds. Shorter times don't harden out the film in exposed areas, while longer times shorten the curve of the material (i.e. they result in excessive contrast). The process is incredibly sensitive for small variations in exposure time. E.g. an exposure of 40 seconds instead of 30 gives a much shorter/steeper contrast curve. The contrast curves used to fashion the digital files and transparencies need to be calibrated to one specific exposure time and that time should be used consistently. Use the shortest exposure that reliably produces both a deep black and pure white (with sufficiently hardened polymer) in a single print. For comparison: the DK3 photopolymer prints at least 4 to 5 stops faster than New Cyanotype, the fastest photographic alt. process I print with! This also suggests that the film is much more sensitive to fogging/stray UV light than many sources suggest - some say you can safely work with it under moderate fluorescent lights or in normal room lighting, but I severely doubt this. Use safe light with no UV at all only.
- I'm not sure yet about a good anti-halation backing. The photopolymer is of course largely transparent, and so is the PVC backing material I use. This means that the light falls through the plate, onto the backing of the printing frame. From there, it could bounce back again, albeit diffused, and expose the film from underneath. This would compromise the depth of the intaglio as well as resolution. A collimated or point light source would probably prevent this to some extent. In my setup, I'm looking for a non-reflective backing material on which I can place the plate. For now, I'm working with either white copying paper (which seems less than ideal to me) or a sheet of fully exposed and developed 8x10" x-ray film. This is one of the parameters that currently worries me.
- I made a 'stock solution' of 100g cleaning soda per liter of water. I dilute this 1+9 before developing a plate, which saves me the time of dissolving soda every time I want to make a plate. It's also more consistent and precise than measuring the soda separately for every development session. I develop 2 small (10x15cm) plates per 0.5L developer maximum; by then, the developer is slightly milky with dissolved polymer and I discard it. For slightly larger plates (15x20cm or 20x30cm) one liter of developer processes 2 plates as well.
- I found development time and temperature to be quite non-critical. I use tap water, which is about 12-14C here and I develop for 10 minutes, without agitation, except for the last few seconds, when I agitate by lifting the tray a few times to wash away the polymer that sits on top of the plate. I tried developing for 6 minutes, which seemed to be on the short side, and I also tried 14 minutes, which produced results completely identical to the 10 minute development time. See below under 'problems and solutions' for further remarks on development and alternative schemes! Instead of 10 minutes 'stand' development without agitation or brushing, it may be more reliable to develop the plates for 3 minutes with constant agitation by lifting and dropping the tray, as with photographic paper.
- I have had some issues with quasi-dissolved polymer sticking to the surface of the plate. I try to prevent this by dunking the plate into a tray of water and then agitating the tray by lifting it and putting it back, rolling the water over the plate (as you'd do in developing a sheet of film or photographic paper). This seems to work fine; if it doesn't help sufficiently, I return the plate after drying it with a hairdryer to the tray of water and wiping it gently with my fingertips to remove the traces of polymer. However, I find that this issue occurs mostly (or, virtually exclusively) in larger areas of the plate that are underexposed (resulting in open-bite).
- The stop bath I use is just a tray of water with a dash of cleaning vinegar added to it. I put the plate in it after washing it (see above) and agitate for a few times. I generally leave it in the stop bath for only a minute or even slightly less. This timing doesn't seem at all critical.
- Hardening a plate takes about 3-4 minutes with the plate at only a few cm from the UV light source. This is much longer than the 'about twice the time of the original exposure' cited in other sources. Either my exposure times are way off (entirely possible, but the longer exposures didn't work for me; see above), or something else is going on. Either way, it's easy to see when a plate is hardened sufficiently as it'll turn a deep blue color, instead of the pale greenish blue of unhardened DK3 photopolymer.
- At the edges of the film, there are usually some frills of polymer film, as I try to trim the film just slightly larger than the plate (perhaps half a millimeter) after laminating it. These frills/fragments can be shaved off with a bit of sandpaper wrapped around a block. This helps to smooth the edges of the plate as well, making it easier to wipe them and prevent black lines around the print - although I don't worry too much about those. The frills can be ground off with some fine sandpaper wrapped around a block of wood after hardening the plate.
Problems and solutions
Here I will list some of the problems I've run into and offer some thoughts that may solve these issues. It's a work in progress, so I can't guarantee these solutions to be completely reliable.
- One of the most persistent and frustrating issues has been white areas or blobs on my prints. Further inspection of the affected plates shows the intaglio to be less pronounced or degraded in those areas. At first, I suspected local overexposure of the plates, so I switched to processing (laminating, exposing and developing) the plates under red LED safelights. This seem to alleviate the problems substantially, particularly in small (10x15cm) plates.
- With larger plates (20x15cm), the problems with the lighter ares persisted. These areas are big, from 10% to 25% of the plate being affected, which rules out e.g. newton rings (which, I have read, are supposed to cause dark areas instead of light ones, anyway.) Apart from local exposure hotspots, development is another parameter that could be suspected. I ran some more tests with different development schemes to see if I could solve the issue. I tried brush development, soaking the plate for 1 minute in the soda developer and then brushing it very gently with a soft, synthetic sponge for another minute. For small (10x15cm) plates, this seemed to work like a charm: more or less perfect prints! But with 15x20cm plates, the problems with the light areas got only worse. I suspected that the brush time needed to be scaled up along with the plate surface, so that the amount of brushing would be the same for a given plate surface area. But alas, no luck. 1 munite soaking followed by 2 minutes of brushing on a 20x15cm plate (twice the surface of a 10x15cm plate) resulted in the same, or even worse light areas, particularly in the middle of the print. Close inspection made me suspect that the brushing actually caused the top layer of the photopolymer to be polished off locally. It makes sense that particularly the center of the plate would be affected, as that area receives the most brushing (if you brush the edges, you hit the center as well, particularly with a large sponge). So I opted for another route:
- Another possible cause for the random light spots I got with the 10-minute stand development scheme without brushing or agitation, is local variations in dissolved photopolymer and maybe variances in pH as well. Uneven development due to local variations in developer chemistry are a known problem with stand development routines for silver-based photographic materials and it seems plausible that this would happen with photopolymer as well, despite the apparently simpler chemistry involved. So I tried a third development scheme: constant agitation by lifting the developer tray during the time of development. Logically, I would have to develop as least as long as when I'd brush the plate, but shorter than with stand development due to the mechanical action of the alkaline solution on the plate surface. I did a quick test, inspecting the plate after every minute of development with constant agitation, and after 3 minutes, the plate looked sort of good, insofar it's visible under a red LED. After hardening and printing the 20x15cm plate, the print seemed to be close to perfect in terms of evenness! So at this point, I've arrived at the preliminary conclusion that 3 minutes of development with constant, firm agitation but no brushing or other physical manipulation of the plate works well with this particular photopolymer film and exposure regime.
- Another problem I've had early on during testing was warping of the plate. I found two causes, which are easy to resolve: heating the plates too much (keep in mind I'm using 1mm PVC sheets as a backing), causing them to warp, and excessive pressure during pulling the print on the press.
- The edges of the polymer plates remain a sensitive subject - literally. Early on, I had small fragments of the brittle, hardened polymer flake of the edges of the plates during wiping, causing jagged edges on the prints. The holes left by the flakes that fell off would hold a large amount of ink, making the problem quite pronounced in the final print. The main cause I've found so far are insufficient adhesion of the polymer to the backing plate. The solution is simple: let a laminated plate rest for at least 24 hours (preferably >36, I'd say) before exposing and printing it. Secondly, it seems to help to roughen the PVC backing sheet with some very fine (400 grit) sandpaper before laminating the film into it, so that the film adheres to the plate better. After exposing and hardening the plate, the edges can be polished a bit using the same 400 grit sandpaper to smooth them, so that they hold less ink. This way, the print edges can be made quite clean and for my purposes sufficiently unobtrusive.
- Abominable blacks: too light and/or false biting. Getting good black is a challenge with intaglio printing, as etched out areas of a plate tend to get wiped clean of ink during wiping. Some intaglio (miniature bumps) need to be present in black areas, holding the ink and preventing it to be wiped off. Getting the right intaglio for a clean black has been a quest and so far I've come up with the following process parameters: the inkjet positive is printed using the matte black ink, which is more opaque to UV light than photo black. A print resolution of 1440 creates sufficiently small dots on the Epson 3880; the coarser texture of 720 dpi (the native resolution of a single channel on this printer) should theoretically create an intaglio pattern that holds even more ink, but a very deep and nearly even black seems to be achievable with 1440 dpi as well, which has the added benefit of a higher resolution in the non-black areas of the print. Additionally, the coverage of the dots int the black areas is an important parameter: you want just enough bumps in a black area to hold enough ink, but not so many that they create obtrusive light 'islands' in the black. I found that with my print setting, light source and processing regime, a 'black point' of about 76% is the optimum.
- I've wondered a few times if a finer intaglio screen (at something like 2000 or 3000 dpi, which I'm unable to make with an inkjet printer) would enable an even more even black along with more detailed prints, but I haven't pursued this route. It would also necessitate a dual exposure workflow, exposing the plate separately with the intaglio plate and the image positive. I imagine superior results can be achieved this way, with attention for calibration of the process, of course. The advantage would possibly even more pronounced in the highlights as opposed to the blacks. With an inkjet positive with 'built in' intaglio for single exposure, the image consists of black dots only, not using the light black and light-light black channels of the more upmarket printers. This results in the highlights consisting of relatively few, but completely black dots. In the final print, this is echoed: highlight areas, when viewed at close distance or even through a loupe, are in fact very tiny dots with a lot of white space between them. When using the light and light-light black channels of the printer as well (or even up to 7 black channels as with piezography-converted printers), the light areas consist of many more dots per surface area, but of varying darkness, resulting in a smoother appearance when viewed at close distance. But this would only be achievable when used in combination with a separate intaglio/stochastic screen.