silkscreen printing: first pancakes and photoemulsion
a few weeks ago fr4gmentedidol and i screen printed his artwork onto t-shirts for a group of roommates we shared once upon a time. we did a three-color print, using a vinyl cutter to create the masks (which we adhered directly to the screens).
they came out phenomenal! the vinyl mask technique was pretty robust and resulted in a consistent product, but it has its limitations; the black layer in particular was pushing the limits of how much detail can be captured. the scales on the creature's belly weren't connected to anything else, and the eyes and chins had some islands as well. after printing just eight shirts, bits of the black mask were beginning to fall off. i got the taste for screen printing and i want moar. so i've begun learning how to create high-resolution silkscreens with photoemulsion and UV exposure. fr4gmentedidol is the progenitor of the "first pancakes" theory of making: every new project is like making pancakes. if your first project artifacts aren't the quality you hoped for, don't disparage. those are just the first few pancakes that help you get the skillet to the right temperature, and you can snack on them while you continue cooking a plate full of gorgeous golden-brown syrup delivery disks for your hungry houseguests. well folks, this weekend i made a lot of first pancakes. still, i'm pleased with my progress.
how it works
a silkscreen (or just "screen") is a simple aluminum rectangle, with a tightly-stretched fine mesh across the surface. there are different grades of mesh; this weekend i used an 18"x20" 230-count screen. the screen is lowered onto a substrate (usually paper, canvas, or fabric) and ink gets pushed through the mesh with a squeegee.
photoemulsion is a green, UV-sensitive goop that can cure into a hard shell. it gets applied onto the entire screen in a few even coats, then allowed to dry (but not cure) in a dark cupboard. the coated screen should be kept away from light until it is ready to cure (or "burn"). after it is dry, parts of the screen should be covered (or "masked") so that when you do expose the screen to light, the masked parts remain uncured. the easiest and most precise way to do this is by printing a black and white image onto a transparency sheet, then pressing the sheet against the screen. finally, the coated and masked screen can be burned. this involves shining UV light at it until the exposed emulsion has cured into a hard shell. then the transparency can be removed and the screen can be washed out under running water -- the portions that were masked by the transparency will wash clean, allowing ink to pass through those areas (and only those areas) when squeegeed. i set up an exposure chamber in my closet. it's a 60W 405nm UV light, positioned 4ft above the screen. i place a matte black foam block under the screen and a pane of glass (with printed transparency) over the screen to ensure the transparency is pressed firmly against the emulsion, so no light can leak onto the masked portions.
artwork prep: halftones
ultimately, a given part of the mesh is either exposed to the UV light (and therefore will cure into a hard shell and will block ink) or it isn't (and therefore will wash clean and ink can go through). it's not possible for a given part of the screen to be partially-porous. this means the image you print onto transparency sheets must be black anywhere you want color and white anywhere you don't -- no gray. to overcome this, you can use black dots on a white background (or vice-versa) to achieve color tones which appear partially-opaque (i.e., halftones, hence the name 'halftone dots'). by controlling the size of the dots, you can create a full gradient. other halftone techniques exist as well, such as hatched-line halftone or circular halftone, but halftone dots are the most common. here's the image i made for my first test burn:
with a 230 mesh, i probably could have done slightly finer-detail halftones. but i'm still getting my sea legs, so i didn't want to push it.
burning: lessons learned
so i burned my first pancake. (pause to appreciate wordplay.)
tips: getting even coats of emulsion is important, and a scoop coater helps a lot. pull the scoop in one smooth, fairly quick motion. coat your screens in a dim room and immediately load them into the dark drying cupboard. always keep your screens normal to gravity after coating them and until they are fully cured. your transparencies need to print really dark black. my laser printer can't get dark enough, so i went to fedex. after washing out the uncured portions of your screen, give it some extra curing time to make it more durable.
getting timing right is going to require trial-and-error. i settled on 6.5 minutes, then wash out the screen, then another five on each side.
printing on paper
i picked up some watercolor paper at the arts store and did some prints with my turquoise and copper inks. unfortunately, i'm not really pleased with any of these pancakes, but i did learn some lessons for next time.
paper is much more finicky than fabric, and 230 mesh really soaks up a lot of ink. i kept accidentally getting ink on the back of the screen, which is game over until you clean the screen again. i need to practice filling the right amount of ink into the screen and applying even, firm pressure for each pull.
i've already got another fun monochrome design. it says 'tree house screen printing', although you might have to unfocus your eyes to see the 'screen printing'.
and i'm working on a warhol-inspired la roux portrait. this one will be at least five color (but only the black layer features halftones).