The CAFA lithography studio is open again after the Chunjie holiday and this month I have been working on learning how to print a consistent edition from a stone.
This entry is a bit full of printing jargon. I will try to explain some of it because I find the printing process itself fascinating. I will also write a more basic entry about lithography in general and provide some links to other sites on lithography as soon as I get a chance. This particular entry is about the process of “troubleshooting” the problems I encounter as I am printing an image from a stone.
What is an edition?
To print an edition means to print the image on the stone multiple times without variation in the amount of ink, the clarity of the image, or the overall quality of the print. In a good edition there should be no flaws in the image, roller marks or inky thumb prints (this is a lot harder than it sounds since I always get ink on my hands when inking the image and have to be careful not to transfer it to the paper.) This means that to pull an edition of 15 identical prints, for example, I need to pull about 25. The first 3 prints I pull are proofs and help determine if the image is drawn correctly and how many passes with a roller the image needs each time for the image to be well inked. Although the press has to be reset between the proofing process and printing the final edition because the stone is further chemically processed between these two steps, I can also get a feel for what amount of pressure is needed in order to pull a good impression.
Once I proof the image on the stone, decide that the image is finished, and determine the number of rolls the image needs to be properly inked I then process the stone again (see explanation about the chemical process of lithography). I am then ready to print the edition. Even an experienced printer pulls some bad, or inconsistent prints, which are not included in the edition. I have been printing around 30 sheets of paper, which results in somewhere around an edition between 15 and 20. As I begin to perfect the printing process I hope to lose only a couple prints, as I usually do in etching.
Troubleshooting the Printing Process
The last couple of weeks has been an interesting learning process as my teacher and classmates at CAFA help me find the places where I am making errors in the way I am printing resulting in poor printing quality.
Part of my problem is that I am learning a new process and part of it is that I don’t always understand what I am told the first time because my Chinese lithography vocabulary is still pretty shaky. When I started learning little bit of lithography at the University of Michigan my biggest problem was that my image overinked and filled in so that I couldn’t pull multiple impressions (aka. a copy of the image on the stone or a print) from the stone. I have continued to have that problem at CAFA, but I finally think I have untangled the problem.
The image on the stone was filling in too quickly
The first thing my professor, Li Xin, suggested was to try pulling only 15 impressions from the stone before chemically processing it again (re-establishing the chemical differences between the “oily/inky” and “wet/blank” parts of the stone). Once it is chemically processed another 15 prints can be pulled. By pulling 30 prints at once the differences between the “oily/inky” and “wet/blank” parts of the stone were breaking down, causing ink to stick to the areas of the stone which were supposed to be free of ink and making the image resolution quickly deteriorate.
The white areas of the stone were becoming gray
This was happening because a thin film of ink wasn’t getting washed off of the areas which were supposed to print white, essentially leaving an ink scum which lowered the contrast of the print and also hastened the overall deterioration of the image (as with the problem above). Adding a little bit of clean gum arabic to the water that was being used to sponge off the stone in between rolls of ink kept the whites of the image much clearer. My teacher often adds a significant amount of paint thinner to the water as well, but I prefer to go without if at all possible since there is no ventilation in the studio and paint thinner is very hazardous to our health.
Some prints are much lighter than others even though there is no variation in pressure of the press
It seems obvious, but I hadn’t realized that when I proof the stone I should count the number of times I roll ink onto the stone. Whichever impression looks best tells me the number of passes I need to make with a roller for all of the impressions in the edition.
I also needed re-ink the roller after every two passes and to add ink to the slab (the square of ink that is rolled out on stone or plexiglass in order coat the roller evenly) after every three impressions so that there was always a consistent amount of ink being transferred from the roller to the drawing on the stone.
How to know if the pressure is correct
some of the prints I made looked all right but I didn’t know how to tell if the pressure was correct or not. Was the print light because it wasn’t over-inked, or was it light because there was too little ink, or was it light because the pressure was to light? I began to figure this out as I looked at my classmates’ prints when they were trying to determine if they had pulled a good print. You can tell a good impression from one with too little pressure because the grain of the stone should be clear and crisp. To light a pressure leads to a light and blurry print.
There are lighter and darker bands or stripes running across the stone
This can be the result of a number of poor inking and printing techniques, all of which I have managed to do over the last month.
Sometimes the bands result from the lap marks made by the roller. A lap mark occurs when the roller has transferred ink onto the stone and off the roller, leaving a less inky spot on the roller, or transferred an inky area of the image back onto the roller, leaving a over-inked area on the roller. If the roller is then dragged back across the image in such a way that this new mark on the roller is transferred back onto the surface of the stone, it leaves a lap mark, or a place where the contact between the roller and the stone has overlapped. This is easy to see in etching and monoprint where the roller is smooth. It is harder to see on the spongy lithography roller but it can still happen if the roller is always rolled in the same direction and then rolled back. To solve this problem it is best to pick the roller up and let it spin at the end of each roll. It is also better to ink the stone from two directions if possible so inconsistencies in the distribution of the ink gradually even out. It also helps to make sure that when rolling up the slab you turn the roller so that it creates the most even surface possible.
Once I also got a white under-printed stripe because the sheet of paper that protects the piece of paper being printed from the grease on the plastic cover (that the pressure bar of the press slides over in the printing process) had slipped. This meant that part of the stone had more pressure on it than the other part. Even something as thin as a sheet of paper can change whether the pressure settings on the press are correct.
The image “rolls up” or accumulates ink too quickly, although the white spaces now stay white
I am used to the smooth rubber rollers used in other printing processes which are cleaned after each use. Our litho rollers can be left for a week with ink on them, perhaps because they are spongy. THis means that when I go to add ink to the roller I add far too much ink, enough my teacher says to print an entire edition. No wonder my prints are too dark! This was an easy problem to solve.
Despite doing all of this the stone is still filling in to quickly
So I found myself still struggling with the printing process at the end of this week and wondering what I was missing. I had watched my teacher demonstrate, taken notes, looked up the words I didn’t know in the dictionary, and been rescued by my classmates a couple of times when they saw I was doing something wrong.
My teacher watched me inking my stone (for the third time) and caught my mistake. The stone is wiped first with a wet sponge and then with a damp sponge between each pass of the roller. I had been literally wiping it with a wet sponge and then a damp sponge. This left tiny water droplets across the image which caused ink to accumulate on the roller, which in turn made the ink bloom, or blur so that it filled in the image and also made the transfer of ink from the roller to the stone spotty rather than smooth. The wet sponge should actually be wrung out till it is damp, so that when you squeeze the sponge only a couple drops of water fall from it. THe damp sponge should be wrung out as hard as possible so it is almost dry. This leaves the stone slightly damp, and maintains the water balance in the white (absorbent) areas of the stone not covered with ink, but leaves the inky areas almost dry, and therefore much more crisp.
Once I figured this out I finally began to pull consistent prints!