Well, I promised that I’d write about my latest foray into photopolymer printmaking and so here goes!
To start with, perhaps I’d better explain what photopolymer is. As the name suggests, photopolymer is a light sensitive polymer. The material has been used in the commercial printing industry for years but in the last couple decades printmakers have adopted it and used it in a variety of ways to create original prints. I have used it myself and refer to it as solarplate because I use the sun to develop my plates. I first came across it when a good friend and fellow artist, Jon McLeod, was doing a residency at Highland Printmakers. I had just come back from travelling extensively overseas and was ready to create a body of work based on my travels. I wanted to include text and maps combined with my collagraphs but didn’t know how to. Jon suggested ImageOn film or photopolymer plate. He gave me a bit of a demonstration and I went off and bought a book on the subject. I basically taught myself everything I know (not a lot!) and have been able to make basic relief and intaglio plates using my photos and text which I then convert to pure black and white on photoshop and print out onto a transparency. This is then placed on top of a steel plate which is coated on one side with a light sensitive polymer (you can buy them from printmaking suppliers). The black part of the design blocks out the UV light and the clear parts let it through. Where the light hits the plate, the polymer hardens and where the black parts mask it, it stays water soluble. The great thing about it is that you can then wash out the black parts using warm water (no chemicals needed). The final stage is to expose the washed plate in the sun for a good hour or so to cure it and then it is ready for printing.
You have to do test strips to determine how much time the plate should be left in the sun and of course, the sun’s strength can vary due to the time of day and the season and you do actually have to have some sunshine in the first place! Many a day has been spent scrutinising the sky for a gap in the clouds so that I can develop my plates. I’ve actually got some good results with relief plates but my intaglio plates tend to have large areas of ‘open bite’ due to the fact that I can’t get mid-tones.
Anyway, I’ve been aware for a while that you can make really interesting photopolymer plates which will retain all the tones and fine detail of drawings and photos and will replicate the look of lithographs, etchings, drawings etc. Fortunately for me, Björn Bredstrom and Christina Lindeberg are experts in this field. Christina spent some of her valuable time teaching me to make the initial test strips today.
But…let’s not get ahead of ourselves! First you have to create the image that you intend to make into a printing plate and before you do that you need to prepare the transparency. This entailed using acetate intended for lithography. You need to roughen the surface of it to be able to draw onto it. This is a very satisfying process which involves wetting a large lithographic stone and squeegeeing your acetate onto the surface so that it doesn’t move about. You then add carborundum grit and water to the topside and take a smaller lithographic stone and grind it over the whole surface in a figure of eight for about four minutes. This gives you a surface with an even bite to it. You can then work on this with acrylic paint, graphite, tusche or any other light fast material. I used 6B and 4B pencils to create the transparency below.
The next step is to determine how long you need to expose your ‘raster’ for. I don’t know what the English name is but a raster is the Swedish word for an acetate with a random dot pattern on that replicates aquatint. You use it to pre-expose your plate before you expose it with your design. The tiny dots mean that you can get fine detail, mid tones and large areas of black without having ‘open bite’ (when you can’t avoid wiping out the ink from large areas of dark tone on your plate because it is completely washed away). I can’t explain it better than that so please google for further details if you haven’t already fallen asleep!
Christina helped me to make the initial test strip and Ida photographed the whole process (she is going to let me have copies) and made notes because she wanted to learn too. We had to cut a piece of the photopolymer plate and then mark a sheet of paper with sections and the timings written underneath. The numbers look odd because they are units not actual minutes and seconds.
I forgot to mention that we are not using the sun. We are using a rinky dink all singing all dancing light box!
You also have to make sure that you don’t expose the plate to light whilst you are in the process of preparing it. It is not so sensitive that it has to be done in a dark room but you do need to keep it undercover when you are in between stages and it is best to cut it in a very dim room. Once we had cut a strip of plate, we then put it in the light box and lowered the glass down onto it, set the vacuum pump to make a good seal and then exposed the whole plate for 1000 units of light….what about the ‘raster’ I hear you ask? Yes, well, we forgot all about that and only remembered when we went to cover part of the plate to start the tests. Whoops! We cut another strip (it’s expensive stuff so you learn a hard lesson when you make mistakes) and this time we laid the ‘raster’ over the top of the plate and then lowered the glass and set the vacuum. After the initial exposal to 1000 units of light, we then covered the marked sections at 100 unit intervals so that one end of the strip had been exposed to 1000 units and the other end had had 1900 units. This took quite a long time!
Next we had to develop the strip so we took it to the wash room and under a yellow light we sat it in a tray of warm water (room temperature) for a minute and then a further minute was spent gently brushing the surface of the plate under the water to remove the unexposed particles of polymer (the black dots of the ‘raster’).
We then had to dry the plate. You can use a hair dryer but here we have a great little drying box. After 5 minutes in there, the plate needs to be cured with a full dose of UV light so back it went into the light box for 15 minutes. Phew!! What a process and it was only a test strip.
After lunch my job was to ink, wipe and print the strip to see which part gave us the best black. The part that was blackest would indicate the amount of units of light needed to expose the plate. Unfortunately the test strip was inconclusive because we realised that the ‘raster’ must have moved each time we lifted the glass screen. Blast! Björn also suggested that we clean the sensor in the lightbox before we made another test strip. This time he told us to divide a strip of polymer into three segments and expose it at 750, 1200 & 1500 units. From that we should determine the range that we would need to make a further test strip. We should stick the raster down with tape so that it didn’t move when we opened the glass each time. The numbers seem a bit random and this would also mean going through the process described above twice and it was now 4pm but Ida and I decided to do as we were told in order to be ‘professional’ 🙂
Thankfully, the three segments showed us that 1200 units gave a lovely velvety black tone.
Björn told me that I needn’t make a further test but I should expose my plate to the raster for 1200 units and remove it and expose my design onto my plate for the same amount of units.
So…I went back and cut a piece of photopolymer plate to the right size and put it in the lightbox with the ‘raster’ on top of it, the glass down, vacuum on and exposed it for 1200 units. I then took away the raster and replaced it with the transparency with my drawing on and exposed that for 1200 units. I went through the developing process, drying process and curing process and after about an hour, the plate was ready to ink, wipe and print. I could see that there was a delicate design on it and I was really excited.
I printed the plate and it is just amazing…you get a perfect copy of your drawing! The only slight downside is that I don’t seem to be able to get a ‘white’. There is an overall grey tone to the print. This could be to do with the process but I suspect that the timing on the exposure of the design needs tweeking. I’ll ask Björn and Christina when they come in tomorrow. I’m now really excited about the possibilities. I am wondering if I could do a reduction monotype on acetate and instead of printing it, I could allow it to dry to make a transparency that I could expose to the photopolymer and then get a plate with all the beautiful marks that you get from monotype but that you can print repeatedly…the possibilities could be endless.
The other thing I need to do is to work out how I can transfer this process to my studio at home. I have a book that tells you how to make a lightbox and Björn says that he has had good results just using an overhead bulb or an anglepoise lamp (the light has to be uv or ‘cold’ light) but you have to make sure that the light stays at a fixed point above the plate and the distance from the plate has to be the same as the diagonal length of the plate in order for there to be an even coverage of light. There is also the small matter of the litho stones and preparing the transparencies but I am sure that improvisation might be possible. Tomorrow I am going to make a transparency using monotype techniques and ink.