Screenprinting Info and Halftone Links
Silkscreen with Photo-Emulsion Jenny Schmid
Positives University of Minnesota
Making the Positive
RULE #1: There are no grays in screen printing- just black and white and dot patterns to give the illusion of mid-tones. The screen hole is either open, or filled.
The resolution (detail) of you image depends on a few things:
1. Your screen mesh count, or the frequency of the holes. One might think that this would be ideally very high, but you are also balancing that with the tendency for ink to dry in smaller holes, and the amount of ink that can be pushed through the mesh. Screen count for our screens tend to be from 190-230. Lower count (bigger holes) is better for fabric, as fabric requires more ink.
2. If you are using a half-tone, the frequency of dots for the half-tone. A higher frequency will give more detail but it exists in relation to your screen holes. See attached handout for half-tone directions.
3. Your printing technique (light flood-coat with a bead of ink, hard pressure for printing at a 60 degree angle) and the thickness of ink (milkshake! Not pudding- thin with water!!) and expedient printing (print fast, don't let ink dry in screen).
4. Proper set-up: sharpness of the squeegee, cards for bounce (this can effect crispness of image).
For digital positives:
-Print on transparency on Sue, the experimental printer. You can book a time at the DSB in advance, handouts in the DSB remind you of the process
-Print on the HP platemaker with vellum from the photo crib (do not run plastic through this or other materials, you will kill our new toy). Note: As of Fall, 2012 we are working to get this beast running.
For manual positives:
Draw with opaque materials on transparent or semi-transparent media. Vellum should be the most opaque material you use for this media.
Mylars: Duralar Wet Media (for ink), Frosted mylars with any opaque material: black pencils, paint pens, etc. Also: litho-coal washes- basically a toner wash to create the illusion of a wash with dots- best used with a clear wet media mylar, like duralar.
Flats can also be made with Ruby-lith, a film-opaque material to make stable block-outs for the photo-emulsion process. If you like how the stencils look, or want to be efficient with your time, this material is for you. You can also make a stencil image and use screen-filler to keep blocking out more area and printing, working reductively to avoid extra work.
Size: Maximum print size for our screens- leave at least a 2" border on each edge, minimally. Printing too close to the edge will cause big problems and possibly screen damage.
1. Degrease your screen, dry it and lay down newsprint around your work area.
2. Stir warm Ulano emulsion in darkroom without making bubbles
3. Pour a bead into a scoop coater over newsprint (do not get emulsion on table)
4. Set screen at an angle
5. Tilt the scoop coater, sharp side making contact with the screen
6. Once the emulsion has made contact with the screen, pull upwards steadily at medium speed.
7. Place on rack in heat unit and remove when dry (don't forget it in there and don't crawl in there with it, no matter how cold it is in Minnesota)
8. Pour emulsion back into the container and clean tools in the washout sink area, not the sink in the darkroom as it bonds with the metal and we will spend four million hours cleaning it at the end of the term.
For Silkscreen Exposure:
1. Clean surface of Douthitt and be sure screen is completely dry
2. Lay transparency face up (or tape it to your screen with scotch tape)
3. Lay screen flat side down on top of it
4. Lay rope outside of your screen
5. Shut and secure hinges
6. Turn on vacuum and be sure that it is working. Adjust if not.
7. Set light units/lumens. 24 to 35 at medium is a generally good setting for all media.
10. Turn off vacuum
11. Open unit and remove all items. Be sure you haven't left a mess!
12. Wash out screen with hose. Only use power washer/warm water if it is not removing
13. Be sure to check for pinholes and fill them with screen filler.
14. Tape off open areas, put cards on and print
15. Work reductively if it makes sense- to save time
16. Put screen in dunk tank of emulsion remover and let stand for a few minutes and scrub and put back in. Put on earplugs and protective gear and powerwash.
Powerwashing is most effective if you
a. Constantly move the nozzle at medium-slow speed. Stopping can ruin your screen but be sure to clean thoroughly.
b. Work from top to bottom, so that emulsion doesn't drip into emulsion and bond.
c. Get it out right away after finishing your project. Give yourself enough time to do the job right. Don't screw it up (or face the music).
Screen filler (red) can be painted on, carded on or squee-geed on. It fills the screen holes and prevents the ink from passing through. It is good for those who want to work in a more direct, painterly manner, or for making simple flats. To work more expressively, try experimenting- dab on with textured cloth, wash parts out before they dry or use with drawing fluid.
Drawing fluid (blue) can be painted on, allowed to dry and then coated with a thin layer of screen filler. Dry and wash out drawing fluid with warm water. The screen will open (and print) wherever it was applied.
Litho crayons can also be used to draw, coated with filler and then washed out for that crafty drawing look. (Wash out carefully with mineral spirits).
Haze Remover- Toxic but helps get out stains. Talk to Jenny or grads to use this.
You can find great handouts about creating halftones for screenprinting by Kevin Haas here