Photo-emulsion Screen Printing

Step 1: Photo-emulsion Screen Printing

Sometimes you need to your message out quickly and cheaply. How do you print a ton of t-shirts and patches fast? Here's how I did it.

This Instructable covers the standard photo-emulsion screen printing process, which is great for printing text or images with fine detail...and at the end, you have your own personally-designed entirely unique prints on fabric, clothing, paper, or whatever else you can get under your screen.

The general idea: After stretching fine-mesh cloth over a wooden frame, you spread a thin layer of photosensitive emulsion on the screen and let it dry. You then take a black image on transparent or translucent surface, place it against the screen, and then expose the screen to light. The light causes the emulsion to harden and bind to the fabric. Where the light strikes the screen, the emulsion will bind, making a solid layer. Where the light is blocked (ie where your black image is placed) the emulsion remains water-soluble. After exposing the screen, you spray down the screen with water, washing off the emulsion only where your image was placed; this clear area is where ink will be pressed through the screen when you print. Finally, you lay the screen on your t-shirt, other fabric, or paper, spread ink on the inside of the screen, and press the ink through the screen. If you use textile ink, you can heat-set the ink after it dries, and it'll be permanent and washable.

There are some great Instructables up on the site already for screen printing methods, but there's always room for more. For this project, I went with a ready-made screen and images printed in black on transparencies.

Check out Screen Printing: Cheap, Dirty, and At Home for info on making your own screens and using the sun to expose your photo-emulsion.

Threadbanger has an excellent D.I.Y Screen Printing Instructable which covers making screens using old embroidery hoops and using Mod Podge to put your image on the screen.

How to Silk Screen has a good overview of the photo-emulsion process.

Step 2: Gather your materials!

What you need:
@ a screen
While I used a ready-made Speedball frame for this project, making your own screens is cheaper, and not hard to do. Take a look here and here for great tips on making screens.
@ a printing squeegee or piece of cardboard with a smooth, straight edge

@ photo emulsion and sensitizer
I used Speedball diazo photo emulsion and diazo sensitizer; the exposure times I list later in this Instructable are for this formula. If you use another type of photo emulsion, be sure to read the directions and test to make sure you have the correct exposure times.
@ screen filler fluid (again, I'm using the standard Speedball stuff)
@ photo emulsion remover (for taking the emulsion off the screen so it can be reused)
@ screen printing ink for fabric

@ a light table
-or-
@ light bulb (at least 150W, clear incandescent), light bulb socket with reflector, clamp, and cord

Miscellaneous useful things:
@ pushpins (at least 4 per screen)
@ chopsticks, popsicle sticks, plastic spoons -- for mixing and putting emulsion & ink on the screen
@ small paint-safe cups
@ masking tape (water-resistant tape is best)
@ regular transparent tape
@ lots of newspapers (to keep everything else clean!)
@ a book or piece of thick cardboard that's slightly smaller than your screen
@ sheet of cardboard that fits inside your t-shirts (if you're printing shirts)

Step 3: Preparing your photo emulsion

Follow the directions listed for your photo emulsion. For the Speedball photo emulsion I'm using here:

Fill Diazo Sensitizer bottle 3/4 full with cold water. Shake well. (The sensitizer was a black sludge on the bottom of the bottle, so mixing it thoroughly required lots of shaking and stirring with a chopstick.)

Pour the contents of the Diazo Sensitizer bottle into the Diazo Photo Emulsion container. Mix until all of the photo emulsion is a uniform color. The diazo photo emulsion starts out as a bright, light blue color. The sensitizer is a nasty black-green color. After mixing, the sensitized emulsion should be bluish-green.

Ideally, you want to do both this mixing step and the screen-coating step in a relatively dark room, to expose the emulsion to as little light as possible.

The sensitized emulsion can be stored (according to the bottle) in a cool, dark place for about 8 weeks at room temperature (70F), or four months in the refrigerator.

Step 4: Coating the screen

First -- lay out newspapers on your work surface, if you haven't already. Sometimes this step is relatively clean, and sometimes I end up with green emulsion all over everything.

Since you'll be flipping the screen over repeatedly during this process, go ahead and put a pushpin in each corner of the bottom (flat) side of the screen. That way, you can flip the screen and set it facing bottom-side down without getting emulsion everywhere. Also, if you don't have a squeegee, you can use a piece of semi-flexible cardboard, so long as it's got a wide, straight, smooth edge for spreading.

Start with the screen bottom (flat) side up. Pour (or glop, as the case may be) a thick line of emulsion across one end of the screen. Use the squeegee to spread it evenly over the whole screen, making a thin layer. Flip the screen over and rest it on the four pushpins. Pour another thick line of emulsion on one end of the inside of the screen and spread it evenly over the screen with the squeegee.

Repeat this process until you have a thin, even layer of emulsion covering the entire screen. (This shouldn't require flipping the screen more than a few times; you want to work quickly to minimize the amount of time the sensitized emulsion is exposed to light.) Do the final spreading step on the inside of the screen, so that you have a smooth surface for spreading the ink later.

Once you're done, set your screen bottom-side down (resting on the pushpins) in a dark place to dry. I usually set mine inside or under a cardboard box, in a closet or closed cabinet.

I let mine sit overnight, but if you want it to dry faster, point a fan at it.

Step 5: Prepare your image

The emulsion on your screen is photosensitive; when it's exposed to light, the emulsion hardens onto the fabric and becomes water-resistant. So, to put your image on the screen, you want a "positive" with an opaque, black image on it (blocks light) and a transparent background that lets light get through to react with the photoemulsion.

An easy way to do this is to make a black & white image with a graphics program, or draw on white paper, then photocopy the image onto a transparency.

For this project, I'm printing up some patches and maybe t-shirts, and my images are just plain black text. I've included the .pdf files I used for my prints.

More ideas:
It's even possible to make a "grayscale" screenprint, where solid black areas on your printed image end up entirely clear on your screen, and gray areas are a pattern of tiny black dots that become tiny clear spaces on your screen. To do this, you'll still need to start with a fairly high-contrast black & white image, then convert it to bitmap. A resolution test pattern (like this classic RCA test pattern) helps with calibration and makes a neat screenprinted image by itself, too.

Step 6: Expose your screen, then rinse

Your screen is tucked away somewhere cool and dark to dry, so the next step is setting up your exposure rig.

A lightbox or light table, with several fluorescent bulbs set directly under a translucent piece of acrylic, allows for simpler set-up and shorter exposure times, but may take some experimentation to figure out what the correct exposure time should be. And hey, there's even an Instructable on making your own light table. Depending on what light intensity you have coming out of the lightbox, your exposure time could be around 4 or 5 minutes.

The setup I used for this project is just a 150W clear incandescent bulb in a socket with a long cord and reflector. A 150W bulb requires a much longer exposure time, but that's fine by me; it gives me a chance to take a break and get all my ink and fabric ready.

Setup:
Before taking your completely-dry screen out, get the rest of your exposure rig put together.
You'll need some non-reflective black fabric, a sheet of glass or acrylic big enough to cover your screen, a ruler or tape measure, the light bulb, socket, and reflector.

With the light bulb & reflector all put together, hang it so that your bulb will be 12 inches (for a 10x14 screen) above the surface of the screen, centered. Lay the black fabric on the ground where your screen will be placed. Have your image-on-transparencies and acrylic ready, and check to make sure you've got the transparencies in the right orientation.

Since you're going to set the screen with the bottom side facing up, then lay your image and the acrylic on top of that, you'll be placing your image so that it's backwards when you look at the bottom side of the screen. This is especially important for text! (Think about it like this: you'll be putting ink on the inside of the screen and pressing it through to print. So the image you see from the inside of the screen is what prints; what you see when you look at the bottom side of the screen should therefore be the reversed image.)

Exposure:
Once the exposure rig is set up, take the dry, sensitized screen out and center it under the lamp, bottom side up. The black, non-reflective fabric should be underneath the entire screen. Arrange the transparencies with your images on the bottom side of the screen, then lay the sheet of acrylic over them to hold them flat against the screen. Check to make sure the distance between the bulb and the screen is correct. Turn on the light, expose for the correct amount of time, then turn off the light. Since I'm using a 10"x14" screen and 150W bulb, I exposed my screen for 45 minutes.

Once the exposure is finished, remove the acrylic and transparencies, then go rinse your screen. The kit directions for this step say "Apply a forceful spray of water (body temperature) to both sides of the screen. DO NOT USE HOT WATER." "Forceful" seems to be the key word here -- even the unexposed emulsion likes to stick to the screen fabric when dry, and using a strong shower spray or the spray-nozzle on a hose seems to work the best. As you spray, you'll see clear areas developing where your images blocked the exposure light; concentrate your spraying on those areas. You can rub the screen lightly with your fingertips, but if your image has fine details, you may lose some resolution by rubbing off extra emulsion around the edges of your image. Hold the screen up to the light; the mesh of the screen fabric should be entirely clear and open in your image areas. If it's not, keep on spraying.

Once your screen is washed out, let it dry completely.

Exposure chart for the Speedball diazo photo-emulsion system:
150 clear incandescent bulb
Screen Size 150W Bulb Height Exposure Time
8"x10" . . . . . . . . 12 inches . . . . . . . . . . . . 45 minutes
10"x14" . . . . . . . 12 inches . . . . . . . . . . . . 45 minutes
12"x18" . . . . . . . 15 inches . . . . . . . . . . . . 1 hr. 14 minutes
16"x20 . . . . . . . .17 inches . . . . . . . . . . . . 1 hr. 32 minutes
18"x20" . . . . . . . 17 inches . . . . . . . . . . . . 1 hr. 32 minutes

250W BBA No.1 Photoflood
Screen Size Lamp Height Exposure Time
8" x 10". . . . . . . . 12 inches . . . . . . . . . . 10 minutes
10"x14". . . . . . . . 12 inches . . . . . . . . . . 10 minutes
12 "x 18" . . . . . . .15 inches . . . . . . . . . . 16 minutes
16"x2O" . . . . . . . 17 inches . . . . . . . . . . 20 minutes
18"x2O" . . . . . . . 17 inches . . . . . . . . . . 20 minutes

Step 7: Print with your screen!

First, take your dry screen and hold it up to the light. If there are pinholes or spots where the emulsion didn't expose and washed out, cover those with masking tape. (Or, for a more durable fix, paint a thin layer of Screen Filler fluid over the pinholes or unwanted open areas and let it dry.)

Wear clothes you won't mind getting ink on, and make sure to put down lots of newspaper on your work surface. This is definitely a messy step.

I've found that screenprinting is much easier with a friend helping, especially if you're printing on fabric. This way one person can hold the screen down tightly on the fabric while the other spreads the ink.

For printing on fabric:
I've used the Speedball or Versatex textile inks for printing on fabric. It's a good idea to test your ink on the fabric to make sure it adheres and heat-sets properly. If you're printing on new t-shirts or clothing, make sure to wash it first. Scrap fabric and remnants from the fabric store make great material for patches. You can also pick up blank t-shirts, tank tops, or other basic clothing from thrift stores.

For printing on t-shirts, you'll want a piece of cardboard or newspaper to go inside the shirt so that the ink doesn't bleed all the way through to the other side. I also usually put a book or piece of cardboard that's slightly smaller than the screen underneath the fabric, so that the screen can be pressed down taut against the fabric.

It takes a bit of experimentation to figure out which printing techniques work best for a particular screen, ink, and fabric. For these prints, I laid the fabric down over a piece of cardboard, then set the screen on top of the fabric and had my friend hold it down. I put a bead of ink on the screen, then pulled the ink down the screen with my squeegee set at about a 45 degree angle. If it looked like I didn't have even enough pressure or missed some areas, I made another print stroke without moving the screen. My results aren't perfect, but they're fine for a set of patches to go on shirts, bags, or whatever-else.

Other tips and techniques:
You can do a "flood stroke" to spread ink over the screen before setting it down on the fabric. For this, you'll need to have your friend hold one end of the screen up away from the table. Put a bead of ink on edge of the screen closest to you. Spread the ink into an even layer using a smooth, light pass with the squeegee. Have your friend set the screen firmly down on the fabric, put your squeegee on the other side of the bead of ink you've just pushed across the screen, and pull it towards you with firm, even pressure. (Again, have the squeegee at about a 45 degree angle to the screen.)

The inks I'm using for this project are pretty old, so they don't flow as well as I'd like. Ideally, you want your ink to be smooth and slippery -- you can add some of the ink bases that Speedball makes, or just mix in a few drops of water.

For printing on paper:
The process is pretty much the same as printing on fabric. I've found the "flood stroke" technique to be more useful when printing on paper than on fabric. I still often use a bit of cardboard under the paper so that I can press down more firmly with the screen, but it's not necessary. Different types of paper will take ink very differently, so experiment a bit to find out what works. Heavy, porous-surface papers tend to work well. Lightweight paper often warps and wrinkles under the ink, and glossy paper doesn't take ink well and tends to smear.

Step 8: Changing inks, cleanup, and heat-setting your prints.

Changing inks:
If your prints have started smudging because there's ink on the bottom of the screen, or your ink has started to dry on the screen, or if you're just ready for a new color, it's time to rinse out the screen. Remove any masking tape on the screen. Hold it under a spray of warm water until the ink is all washed out, then set it out to dry. Pointing a fan at the screen or setting it out where it gets a bit of breeze makes this go much faster. Once it's dry, you're ready to put masking tape back over the areas you don't want printed, then get back to printing!

Cleaning up:
Again, make sure to rinse all of the ink out of the screen when you're done. Ink that dries on the screen will clog it and prevent ink from going through next time you print. Also wash out any dishes or paint brushes you've used before the ink dries on them. Close your ink containers tightly. If you have any photo emulsion left, make sure it's stored in a cool, dark place.

If you're done with your screen and know you aren't going to be printing anything more with it in the future, you can strip off the emulsion with the Speedball emulsion remover. Follow the instructions on the bottle. Wear gloves, and be aware that it'll take a lot of hot water and scrubbing to get your screen clean.

Heat setting your prints:
After the ink has dried completely on the fabric, set an iron on the highest dry heat that the fabric will take. Place a light piece of cloth between the iron and the printed fabric, then iron on each side for 3 to 5 minutes. (I've found that if the ink is entirely dry, I don't really need the extra piece of cloth. I also tend to iron my prints for at least 5 minutes or longer, just in case.)

Finishing:
For patches, I'll usually run a quick zigzag or overlock stitch around the edge of the patch, to keep it from fraying. Check out the "How to Patch Your Clothes" instructable for instructions on putting your patch securely on your clothes/bag/whatever.

If you've printed onto a t-shirt or other piece of clothing, you're ready to go.

Enjoy your totally unique wearable art...and, depending on what you've screenprinted, make a statement at the same time!