Saturday, 4 June 2011

Printing

I'm trying to remind myself exactly how we did things for A Cup of Life. I'd rather put it on the blog so it won't get lost among my files and so that I can pretend other people find it useful.
It was a rather lengthy process and we hit a few bumps along the way. First thing to do, after having all of your drawings done, is to transfer them onto tracing paper or print them out onto acetate. The lines can be quite thin but they must be very dark, as dark as you can get them. This was a bit of a problem for us in some areas when I didn't press hard enough. This resulted in the lines not developing properly and printing out too faintly. For printing onto the china, we had to buy special transfer paper, don't ask me what it is called, which can only be printed on with silkscreen. In our printing room, there are two types of screens and the ones for ceramics has a 95 written on it. Whether printing with special paper or not, the screen must be prepared. The light sensitive emulsion must be applied to it firmly and evenly and then it must dry. Keep it out of sunlight as it will harden. Once the screen is dry, it must be exposed to UV lights. In our screen printing room, there is a huge light box with a vacuum that will do this for you. Place the tracing paper under the screen, making sure to leave at least 5 inches at the edges of the screen, and fasten down the lid of the light box thing. Turn on the vacuum and then the light for the appropriate time. When we did it, the dial was set to 17. The screen must afterwards be washed, with the power washer thing put on gentle. It will clean off any of the emulsion that was hidden by your drawing and therefore not hardened. The screen must again be allowed to dry. If you have a heating rack, place it at the bottom so that it doesn't ruin the screens of others by dropping water on them. Once dry, fasten the screen to one of the printing tables and tape down any areas that should not be printed, this includes the edges. If you have a small scree, a squeegee the appropriate size will do, but if your screen is A1 like two of ours were for the books, the squeegee is attached to the arm of the table. The paints must be mixed using half acrylic paint and half medium. For ceramic printing, the paint is made using glazing powders. There should be directions to follow along with the powders. A mask must be warn when mixing the glazing paint. This paint must be stored in a fridge and will expire in a week. Pace your paper under your screen in the position you want the print to be. Use masking tape and card to mark the corners of you paper so that the next print is in the exact same position on your next sheet of paper. Place your paint in front of your squeegee which you hold constantly at a 45 degree angle. Lifting the screen, flood it by dragging the paint across your print. Remove the paint with the squeegee and place it back down in it's original position. Making sure the vacuum is on and pressing hard but keeping the 45 degree angle, print. For the large screens, you would be using the table arm which you drag across. Once all of your printing is done, wash the screen off with a sponge and dry with paper towel. Remove your screen and power wash on high. There is a solution that must be first applied to the screen to help remove the hard emulsion. Gloves must be used when applying this solution and goggles and earmuffs must be worn when using the power wash, make sure it is turned on and that you turn the tap off once you are done. The screen doesn't necessarily need to be dried before being put away. If you used the ceramic transfer paper, it must be allowed to completely dry. If there are areas or lines you did not wish to print, gently scrape off the paint but try not to damage the thin film on the paper. When we were making plans for our ceramic set, we were informed that the colours red, yellow, and purple had some difficulty showing. For this reason, we chose to print ours in blue. Also, large blocks of colours tend to shift and bleed so we decided to stick mainly to lines. The paper is also only able to sit cleanly on flat areas or on ones that curve in only one direction, like a mug. Our china was rather problematic, especially the teapot Merle decorated. This is why we had lots of tiny designs instead of large ones. The designs must be cut out, leaving about a .25cm or 1/8 inch edge. It is then placed in water and allowed to soak. The paper curls around itself in the water and when it starts to unfold, it is ready. The thin film with the paint on should slip off the paper and stick to the ceramic surface. We found it worked best to not leave the print in the water too long and to not shift it too much or it will loose it's adhesive and no longer stay stuck flat. All the water and any bubbles must be removed from under the film using a tissue. If it is folding into itself or not sticking down because of curves in the ceramic, groves and cuts should help it settle. The ceramics must be allowed to dry and then be put in the kiln. Where the film did not stick, I used a little diluted PVA to stick it down and it worked just fine. The plastic film will completely burn away leaving only the paint. If the ceramic is really old, we were told it might blotch and spot due to dirt trapped under the glaze but we didn't have a problem with that. If you do this at Plymouth Uni, book the kiln in advance. Leave your ceramics in the kiln before 12pm and remove it the next day before 12pm. Do not shut the door of the kiln after your ceramics are in place as, we found out, they might not be noticed and the kiln might be forgotten to be turned on.

No comments:

Post a Comment