how screen printing works

In January I did a screen printing workshop at Sheffield Print Club and since then I have been going screen printing as much as possible so I can start getting good at it. I can’t write about how to be very good yet, but I can write about how the process works, which is cool.

All printing techniques involve putting one or more layers of ink down on top of each other on a substrate, typically paper. The different layers are different colours. All printing techniques allow the creation of multiple copies of the same print from a master version of the design. In screen printing the master version is held on screens. A screen is a fine mesh, that ink can be pushed through, stretched across a frame.

I’ve been making prints from ink drawings. Here’s two ink drawings that are the designs for the 2 layers of a 2 layer print:

Screen 1

I’ve soaked them in oil to make the paper translucent. Now you can see how the two layers align on top of each other. I assume most professional screen printers will work on their designs digitally in some fashion. Designing digitally means you can diddle with the shapes and colours of the layers until you’re happy that it’ll all work together just as you like.

I’ve chosen not to scan my designs onto the computer and diddle with them, preferring to use my original drawings directly and then chuck them away afterwards. This is mostly because I hate working digitally, but it also means I can’t get too precious about the designs and mess around with them endlessly, and it also means I have to make a whole new artwork each time I want to print something. I figure this way is a good way to learn and, although it’s stressful, I kind of like not knowing exactly how things are going to look.

Here is a screen:

Screen 2

The brown gunk in the trough at the bottom of that picture is an emulsion (one kind of liquid evenly suspended in another liquid) containing a polymer (little molecular bricks) that will bind together and form a hard layer when exposed to light. The trough is used to apply a layer of emulsion to the screen

Screen 3

and then the screen goes in a dark warm place so the emulsion can dry.

When it is dry, the screen is placed, emulsion side up, in a vacuum bed. The drawings, soaked with oil to make the paper translucent, go face down on top of the emulsion because the screen will be the other way up when printing so the image will be reversed. The drawings are vacuumed flat to the screen under glass and the whole lot is exposed to bright light for a few minutes.

Screen 4 The whole surface of the screen, except for the area directly beneath the drawing, is exposed, and any exposed emulsion is baked solid. This is clearly visible when the screen is given a rinse to stop the reaction:

Screen 5

The purply area was exposed. The yellowy area was not exposed. Then a power washer can be used to blast off the unexposed emulsion. The baked-solid emulsion will remain as an impermeable layer on the screen. Now you can see where the ink will get pushed through:

Screen 6

The screen goes back into the warm place to dry. This waiting time can be spent mixing up inks. Screen printing ink is acrylic paint mixed with something called a medium. Printing medium is a colourless paint-like substance that helps the paint spread evenly and not clog the screen. I have not much of an idea when it comes to selecting colours. Mostly I just pick some and cross my fingers.

Here is a screen printing bed:

Screen 7

You’ll notice that the bed has little holes in it like an air hockey table. This is a vacuum bed and, like the opposite of an air hockey table, sucks air down through the holes to hold paper flat on itself, which is handy for printing. The screen goes in the big metal frame, which is hinged and counterweighted at the back so you can lift it up and down. This is a complicated printing bed. A simple one is called a clamp bed and is a couple of hinged clamps screwed to a board that hold a screen like this:

clamp

On a vacuum bed the screen is clamped to the metal frame. You tape over the areas of screen around the edge of the emulsion to stop you pushing ink through where you don’t want it. On the bed beneath the screen a clear acetate flap is secured down with tape along one side of it so you can flap it back and forth over the area of bed below the screen.

For this print I fitted both layers onto one screen so I just work with one side at a time. The lightest layer goes down first. Put the ink down and use a squeegee to drag the ink across the design:

Screen 8

This fills the screen with ink. Then you go the other way and push the ink back across the screen. This will push the ink that was in the screen out of the screen the other side and onto whatever is below, which in this case is the acetate flap. As soon as you push the ink out of the screen you want to pull the ink back across it to flood it again so that the screen remains full of wet ink, otherwise bits of ink will start drying in the screen and will crud it up.

After you’ve printed on the acetate flap you can lift the frame up to get the screen out of the way and place a piece of paper beneath the flap to line up the design on the paper

Screen 9

and flap the flap out of the way.

Screen 10

I’ve put some tape down on the bed at the corners of the paper so I don’t have to use the flap every time, I can just line the corners of each piece of paper up with the tape. The frame is lowered back down and the ink pushed out of the screen. This time the ink is pushed out onto the paper.

Screen 11

This process can be repeated as many times as you like, depending on how many prints you want to make. Colours can be changed by using a sponge and water to wash out the screen. A few dummy prints with the next colour need to be done on scrap newsprint in order to get all of the water and old colour out of the screen before going back to good paper.

Screen 12

The newsprint is the wrinkly paper in that photo. When all of the first layers are done the screen can be taken out of the frame and the next one put in for the next layer. In this case the screen is rotated and put back in for the next layer. The first layer is cleaned from the acetate flap and then the process is repeated exactly the same. Screen 13The next layer is going down on the same paper as the first layer (after the first layer has dried).The flap needs to be used every time this time because I have no faith that both layers will consistently line up just using the tape method.

Screen 14

Once lined up the screen can come down and the ink pushed onto the paper and then that print is finished.

Screen 15

Again, you can do as many colours as you want. I’m doing lots of colours at the moment because of learning.

Screen 16

When finished, the baked-on emulsion is removed from the screen using a cleaning product that dissolves it, then you can power wash it all off the screen so the screen is back to having nothing on it and, because I threw away the original drawing, the design is gone forever.

valley pink

If you’d like one of my screen prints they are now for sale in my shop here, alternatively (or additionally) you can join the moon underground club because club members shall receive two prints specially designed for them in their pack of stuff at the end of the year.

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