Since the 11th of May I have begun putting in the practical work that is necessary to learn the collotype process.
As a brief explanation, collotype is a photomechanical printing process, which allows hundreds and thousands of copies to be made from a single plate. A plate is typically made from glass, but can also be made on metal or sized paper, which is then covered with gelatine which contains a light-sensitive solution. Once this covering is dry it is exposed to ultraviolet light through a negative, and then washed to remove the sensitiser.
The gelatine becomes tanned in relation to how much exposure it receives, so that areas which remain unexposed will be soft. Soft areas will absorb water and swell up, while hard areas will repel water. This characteristic means that the hardened gelatine will readily receive oily ink, while the soft areas will repel it. In this way, collotype can be thought of as a kind of photo-lithography.
My initial tests consisted mostly of printing step wedges in order to gauge the exposure, however, despite this, I spent quite some time overexposing my plates without knowing it. As I am already familiar enough with the carbon transfer process, of which collotype is a relative, making plates has been relatively straightforward, and I have experimented with different methods of coating, and different substrates to coat on. So far I have used resin-coated photographic paper, watercolour paper, photographic film, and glass as the plates themselves, and have coated by pouring a 10% gelatine solution as well as brushing on a 5% solution, and also just by soaking in sensitiser as in the case of the film.
The difficult part of this process is the unfamiliar territory of working with ink and making prints on dry paper. In order to try to understand what I should expect to see I have used what little visual information there is out there, as well as by studying related printing techniques such as bromoil and oilprinting.
This first set of photos show what the plate looks like compared to the final print. I have been applying the ink with a mixture of rubber and foam rollers, and in this case, my notes indicate the print was made with a rubber roller. The reason I keep a note is that there seems to be quite a big difference in the grain between the two rollers, the grain of the foam accentuating the grain of the gelatine. As is visible, due to the short roller width, the edges of the roller leave marks where there is a sharp change in how much ink is on the plate. This is something that I have found can be ameliorated with the foam roller, at the expense of a loss of contrast and density, and added grain. This is one of the major problems to be resolved right now.
I continue to test out methods for plate preparation in order to find a quick and easy solution that doesn’t require drying the plates overnight. The above example was made by brush-coating and then drying with a hairdryer, which meant that despite having 7 coatings, the plate was ready to print in less than an hour, from start to finish.
The thickness of the plate apparently affects the amount of grain in the print, but I’m a long way off from being able to test that idea yet.
The problem I have been encountering most recently is the plate refusing to release the shadow areas. I have been soaking my plates in a water/glycerine mixture prior to printing, but not always, and for different amounts of time. But now that I have settled on a standard formula for the sensitised solution, and will be coating on photographic paper, I will also standardise the priming of the plate, in accordance with what the literature says, that being 30 minutes. Another possible solution is to apply more pressure at the printing stage. Because my printing process is simply rolling over the reverse of the paper with a hard rubber brayer, it’s difficult to standardise this part, and up until now I have been wary of squashing the plate, which can also cause it to dry out.
With the remainder of the 5% solution I had been using to brush coat, I poured this 5×7 inch glass plate to see how it would come out. I didn’t bother cleaning the glass at all, prior to pouring, and I also didn’t grind the surface down, which is a practice I have read about and seen being used in order to make the coating adhere correctly. I wanted to see if the 5% solution was sufficient as to be printable, and I wanted to see how necessary the preparation steps are when using glass. Cutting down on consumables and reducing the amount of time to produce a plate are two aspects that will make the process more accessible to future practitioners.
It turns out that this plate printed really well, and the fact that it’s glass helps with handling and inking up. It did appear that the gelatine began to lift in places perhaps, but hopefully this can be solved with a simple wash.
These prints were made with the foam roller, but for some reason the density of the blacks is better than in earlier prints.
The other problem I have been having is the inability to get proper highlights. I made a mask for the above negative, and although you can see the edges of the image that should appear white, they still retain ink. This is quite a contrasty negative, and collotype is supposedly quite a contrasty process, requiring flat negatives, so I expected there to be good highlights in this print.
I suspect that despite significantly reducing my exposure times, from around 15 and 30 minutes, which is what I was using for a similar tissue made for carbon printing, to only 15 seconds, I may still be overexposing the plates. It may also be that because I am not using the traditional sensitiser, I am getting a longer tonal scale.
Another possibility is that my washing process is not enough to completely remove the sensitiser, and so the plates are continuing to be exposed later on, especially in the highlight areas. This is something I will test by attempting to get pure white from an unsensitised, pure gelatine plate, and also by re-exposing a plate that has been washed, to see if there is a difference in the final print.
Besides understanding and taming the process for myself, one of my goals is to make it less esoteric, which seems essential if this once-popular art form is to survive. The use of diazidostilbene instead of dichromate already makes the process non-toxic, but I am hoping to succeed in using a much more common, and cheaper alternative.