Silkscreen with Photo-Emulsion
Jenny Schmid 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 190-240. 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 a photographic-based image
In screenprinting, there are no gray values on your positives- the sceen is either open or closed. There are two ways to simulate tonal range with varying dots to create the illusion of value--a Diffusion Dither or a Halftone Bitmap.
Diffusion Dither Bitmap
Image> Image Size (be sure it is at 150 dpi or higher
Image > Mode> Bitmap. Your output should be the screen mesh divided
by approximately 1.5-2.25, and then round up or down to a whole number. The method should be set to Diffusion Dither. An Output Resolution of 130 will work on a 195 mesh screen.
Image> Image Size (be sure it is at 150 dpi or higher
Image > Mode> Bitmap.
Set your Method to 'Halftone' and your Output Resolution to 720. The Output Resolution should be at least your lpi x 16, and evenly divisible by your printer's maximum output resolution. For example, a 35lpi halftone needs an
Output Resolution of at least 560, but 720 is the next higher resolution that is the inkjet printer's resolution of 1440 evenly divided by 2,
-Print on transparency on the transparencey printer. You can book a time at the DSB in advance, handouts in the DSB remind you of the process
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. Set your screen on the counter or floor with newsprint underneath
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- NO WET EMULSION!
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. (This might be different for us, as bulb may be going).
10. Turn off vacuum
11. Open unit and remove all items. Be sure you haven't left a mess!
12. Get a little water all over and wait a minute or two and then wash out screen with hose. Only use power washer/warm water if it is not removing. Note that the nozzle pulls in and out and turns for different pressures.
13. Be sure to check for pinholes and fill them with screen filler.
14. Tape off or paper cover 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 open areas and bond.
c. Get it out right away after finishing your project. Give yourself enough time to do the job right. Please do this right so we can maintain our screens.
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. Ask us for help if you need to use this.