Screen printing

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Overview

Screen printing is another form of printmaking, meaning the artist creates an object which perfectly reproduces the desired image. Screen printing involves using a tight knit screen of silk drawn over a frame, coating it with a photosensitive material and using light exposure to create a stencil. Ink can then be pushed through the screen to produce an image. The screen image can have as much detail as you want, though you can only print in one color at a time. You can use cheap, non-toxic chemicals to modify the screen's printable area and block out certain parts of your screen. This means you can do another run of printing with a different color and produce multiple color images. Screens can also be combined, mixed and match to produce different imagery.

Materials

Many of these materials I'm happy to provide for people to use. I don't mind people spending these items on their projects, but I do mind wasting them because you don't know what you're doing. Please see me for instruction (I highly recommend the screen printing class) before you try this for yourself.

Drawing - You have options here. It needs to be some sort of ink or wax, something permanent.

  • Acrylic pens - Fine or Medium tip. Whatever.
  • India Ink
  • Rapidograph - pricey, but totally worth it
  • Transparent, double-sided tape
  • Transparency
    • Mylar - it's a kind of high quality transparency, comes in bulk rolls you can cut down later
    • Acetate - pricier transparency. Comes in pads, have to be mail ordered. Really great stuff, doesn't smudge and doesn't crease.
    • Durolar is a versatile new kind of acetate that holds digital work, hand drawing, ink brush, anything that would work on anything else.


Screen - It's like a sieve, or a fine filter. We put emulsion in it, expose to harden, and push ink through it like a filter.

  • There are different kinds, but I like a screen made of ultra-fine silk threads drawn tight around an aluminum frame drawn tight by a machine.
  • $20 - $40 from Ryan's Silk Screen Supply.
  • ~20X20" is considered printable on each screen, a margin of two or three inches around the edge of the screen is considered unprintable, do to the amount of pressure exerted so close the edge on a screen
  • Screens are currently kept in the corner by the race car pinball machine, next to a large box for a Dell monitor. Coated screens go in the box until they are exposed.
  • Screen chemicals
    • Light sensitive photo-emulsion. Thick green goop, hardens with exposure to light.
      • Emulsion is a time sensitive chemical. From the moment it is blended, it is gradually exposing in its container. A number of factors can be used to accelerate or decelerate this process. This may merit its own wiki page, but in summary: Bright light, heat, and moisture cause it to dry and harden and accelerate its exposure rate.
      • We have a batch of the stuff at the shop, in the fridge. Pleaes try to keep it covered when not pouring, and be sure to put it back in the fridge when you're done.
    • Scoop, for applying emulsion to screen
    • Spoon/Ladel for handling emulsion
  • Light Exposure Table - for burning your image into the screen. Should be several inches larger than your screen so that the screen sits flat on the top.
  • Some kind of opaque sheet to lay over the screen as it exposes.
    • You will need to generate pressure to hold your image up against the screen during exposure. Plan to have a couple of pounds worth of weight to sit flat on top of the screen.
  • Printing
    • Sheet of clean, unmarred, plexi-glass, bigger than your screen (tabletop is fine, but harder to clean)
    • Water based ink, whatever color(s) you want your image in
    • Squeegee - varnished wood handle, flat rubber tip
      • Should be as close to the width of your screen as possible, so you only have to pull it across the screen once.

Print medium

      • Paper
      • Canvas
      • Shirt - Must not have buttons, pockets or zippers near or opposite the area you wish to print on. Any of these could pop the screen when pulling the print
        • Multiple colors are harder to achieve, so shirt designs basically need to be one color (probably black for now) for an operation this size.
        • Black shirts, everybody wants 'em, but white ink is never thick enough to print well with just one run. It's always harder to print on black, and white is the only color that stands out on black. Black material is hard to print on, white ink is very, very thin and hard to work with without extra registration and extreme care. So, I prefer not to bother.
    • Unicorn Tears (Optional)- a special blend of bleach and water for black shirts with black imagery.
  • Cleaning
    • Shop Towels OR
    • Rags from torn up old clothing
    • Simple Green - Engine cleaner
    • Baby Wipes - good enough for your baby's ass, will certainly clean up oil based ink.
    • Hose, powerful shower head OR
      • Power Washer is a major expense, but might be worth it in the long run.

Drawing

  • You have options here.
    • Nice ink pens
      • NOT sharpies, they're not thick enough.
      • Rapidographs are slightly more expensive, ($2 each) but they're awesome
      • Acrylic ink pens - cheaper but totally work.
      • Indigo ink, brushes - more painterly than I like to work with, but whatever floats your boat.
      • Photoshop, etc can also be used, to create (or modify) an image, which can then be printed via laser printer onto a tranparency.
  • Draw your pretty picture on a sheet of transparancy, mylar or acetate. Can be any size, but it's better if it fits in one screen. Multiple screen images can be done for large scale work though. For a tshirt, your image probably ought to fit in a 8.5 x 11 sheet of transparancy
    • Do not allow your transparency to be bent, folded, spindled or mutilated. It will show up in the final product.
  • Try to avoid smudging or excess oils on your transparency, like finger prints.

Coat the Screen

Get the screens, emulsion, scoop and dark box ready, this gets complicated and it is time sensitive. Take your emulsion, pour it into your scoop, pouring it across the entire length of the scoop over the round edge so it always drips into the scoop and not over the edge. Have your screen standing upright at about a 30 degree angle in whichever orientation is closest to the length of your scoop. With the hard edge of the scoop, press the scoop up against the screen and tilt it so the emulsion starts to run into the screen. Push the scoop up the screen, applying a thin coat of emulsion to the screen all the way to the edge. Flip the screen over and repeat so now you're applying emulsion to the backside. Press your scoop's hard edge to the screen and push it up both sides without letting the emulsion pour out. This will scoop up any excess emulsion on the surface. Pour extra emulsion from the scoop back into the emulsion bucket. The stuff is kinda expensive, please don't let it go to waste.

Exposure

Immediately after coating the screen, get it in a dark cabinet to dry. It absolutely must not be left in the light, emulsion is light sensitive. It will harden (expose) with light and if that happens, the screen is spent, you have to wash it out and start all over again. Let it sit to dry in the dark box for at least two or three hours. When the screen is bone dry, you can expose it. Take your image on transparency, and apply double stick tape to fix it to the screen. When looking at the frame through the back (screen on the bottom) it should be face up just like you want it to look on the final product, any text facing forward.

Take your screen with image attached to your light table, set the screen face down in the middle of the table. Lay the sheet of black pool liner over the screen. This will trap the light in, helping somewhat with the exposure but mostly just preventing eye damage to anyone who looks at the screen. Weigh it down with what ever's handy to keep the stencil pressed up against the screen during exposure.

  • Exposure Time
    • Sadly, this part is trial and error and depends on your light table. Could take longer, could take less time. You just have to play and see. You can be off by 30 seconds and it'll make your image weird, parts of the image will over- or under-expose. Sucks but it's true. As of August 12, the emulsion seems to take about 3:00 to expose. Now the image will be burned into your screen. Peel your transparency off, you might be able to see a faint outline of your image already, the unexposed areas (the part shielded by the black in your stencil) should be a brighter shade of green. Take the screen outside and wash it out with a hose or pressure washer. Make sure you get the entire screen wet, and then start at lower pressure and work your way up until the water knocks out the un-exposed areas. When you're finished, you should be able to see through the screen where your image is. Most of the screen will retain it's emulsion, except for the parts shielded by your emulsion.

Let the screen dry. Now that it's been exposed and gotten wet, you can let it sit in the light, it's as exposed as it's going to be. It has to be bone dry before you can move on, drying should take about 30 minutes with a fan on it.

Printing

Set your paper, canvas, whatever on a flat even surface. No wrinkles! If you're printing on a shirt, you can use the clothing press. Draw the article over the board, making sure it's flat and there are no wrinkles. I would avoid seams, and absolutely do not attempt to print over buttons or zippers. They may pop the screen and permanently ruin it.

There are advanced techniques for multiple color runs, but for now this article will talk about a single color that does not require registration. Set your screen face down on top of your medium. Get the image in your screen where you want it on the medium . Pour some ink over the screen and distribute it in a strip across one end of your screen.

If you're using the press, the clamps will be holding it in place. If not, either use a separate clamp system or have a friend hold the screen down, their hands holding down the opposite end from where you're standing. Pick up the end of your screen closest to you, and with your squeegee gently push some ink across the screen, pushing the ink into the screen. There should be ink in every part of the screen that contains your image. Set your squeegee down at the top of the screen, the squeegee standing nearly vertical. Pushing down kinda hard, pull the squeegee towards you, the blade of the squeegee pushing ink through the screen onto your medium. Pick the screen up, and behold your image. Take your next medium (another sheet of paper, another shirt) and set it under the screen. You don't have to flood the screen every time, but you can see if there's still enough ink in there. If not, the image will be spotty or faint. Repeat these steps until you've made however many copies of the image as you want. This is called your 'edition.'

Clean up

You cannot let the ink dry in the screen, so use the squeegee and a palette knife to scoop out as much of it the ink as you can. Sponge up the rest for rapid drying, or wash out with a hose. Clean the table top or glass you were working on. A little bit of ink can come through, you don't want that to dry and set.