Photo-emulsion Screen Printing


Step 5: 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.

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.)

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
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biaginn3 years ago
After I removed emulsion from the screen to expose my writing I went to transfer the text onto canvas but the ink did not come through? any suggestions?
Can you expose the screen for too long? Assuming it doesn't literally get burnt, I don't see what else would happen if it were exposed in sunlight for an hour instead of 5 mins?
cynreams3 years ago
ANyone having trouble with exposure times, try this site!! :
JEZIKA LAW4 years ago
I feel i didnt dry my screen enough before exposing as it was a little bit cloudy coloured in areas after washing off unexposed emulsion... is it safe to put it back in the cupboard with a heater for a bit to dry a bit more...or could that over dry it n be difficult to get off later with the special pregasol solution that removes emulsion once wanting to do a new stencil on the screen?
JEZIKA LAW4 years ago
CHEAP N QUICK! ( P.S) The reference to acrylic is refering to perspex in the above tutorial..To Brainnumbc
yayeee i fainally exposeed my first screen from home!
easy as!
My advice is ditch the bulbs n fancy lighting go with natural Uv sunlight, worked a treat!

1. i applied the emulsion with a sgueegee to both sides of the screen as even as possible (Avoid thick build ups and thick small drips) its important your screen is even so the screen dries evenly)

2. Find a cupboard and have blow heater ready in the cupboard, ensure its located in a dimly lit place, Here place your screen to dry over a few minutes, checking it regularly, you will notice areas that r drying faster than others, dont have the heater directly facing the screen its prob not good 4 it. The dried emulsion will appear less glossy.
3. Have you image photocopied onto 3 sheets of acetate, tape these together to create your stencil, this creates a solid black stencil.
Have a large board to set up your foam & screen to later carry outside
Have a sheet of glass clean ready, tape newspaper over it.
Have a piece of foam that the screen can be placed over, (ensure its thicker than the screen frame, possibly another thin piece of flat board over it and place some dark fabric over it.

4. Now your screen is dry, still in a dark place. Nearby in a similiarly dimly lit place ( eg no strong uv lights) Set up all things in step 3
1 place your large board down
2. place your foam, + another flatter surface such as a book on top that fits the image your are making if you feel you need it to create a really flat surface, and some dark fabric over this.have it set up at the lower edge of the board so wen you carry it outside you can lean it against a wall or prop to face direct sunlight..
3. have your acetate stencil handy and some bits of sticky tape to attatch it to screen.
4.Grab you dry screen, placeing it over the foam paying attention to ensure the image to be exposed is resting on enough flat area underneath creating a seal
5 place the newspaper covered glass over this and Breath!
6. now carry it outside to your decided destination where there is bright sunlight ( you may have asomething like a big board set up against a chair with another flat surface on the ground to angle it up upon, as it may be 3;30 in the arvo n the sun isnt directly above you.
anyhow take it out rest it against the "wall" n "floor" directly positioned towards the sun. Remove the newspaper =0)
Usuall exposure on a sunny day is 3 mins
i let it go for 4 n a half it was fine!!
You may notice the emulsion darkening. Which is helpful in telling you its exposed enough.
When you move the glass away you will see your design in a lighter shade letting you know its exposed.

After this take it straight to the hose to wash away the areas of emulsion that didnt get exposed to reveal your fressh sharp stencil!!!!!! Continue to hose closely on high pressure untill you see the actual screenmesh clear of emulsion. Checking closely.

Im waiting now for the screen to dry off n do my first print
now you can get your paint colours prepared n mixed etc =0)
brainumbc4 years ago
Oh duh! The photo emulsion just creates a stencil on the screen! I wish someone would have told me this. All the tutorials I read anyone didn't explain this fact. It just lead you to assume that the photo emulsion chemical was supposed to bind to the fabric of whatever you're printing on
brainumbc4 years ago
Ok I think I understand the black fabric.. so your medium doent get exposed from the back side, but I still don't understand why you need acryllic. I thought you used photo emulsion solution OR acrylic ink to do screen printing.. not both
brainumbc4 years ago
Any why are we even talking about acryllic here? I thought the photo emulsion was the chemical that actually binded to the tshirt or whatever you're printing on? What does acryllic have to do with any of this?
brainumbc4 years ago
Why do you have to put black fabric down? I don't understand
need some help? I'm following the time exposure table . and no matter what I do the screen washes out completely.
kikig2154 years ago
Can I get some help please? Everytime (twice), I expose my screen with the 150W light, my screen gets burnt. I had it 12 inches away for 45min. the 1st time and a little further away thet 2nd time for 45 min. and both times the screen got burnt.
coask8b4 years ago
is it possible to expose the screen outside on a sunny day, instead of using a light rig, like in a similar instructable?
kidburobot5 years ago
i'm really thankful that i discover your site!thank you very much!this would help a lot....
metalfury5 years ago
Hi, great tutorial and i thought the tip about using the pins to raise the screen was very clever. Just some questions if you don't mind? You have placed your positive on the 'bottom' of the screen, back-to-front. Are there any advantages/disadvantages to placing the positive 'inside' the screen, and the right way round? (I have a piece of glass that fits well inside my screen). I was wondering if with your method, light could 'seep' underneath the positive via the 1" gap between your screen and the black fabric? My other queston is regarding the lighting rig. I was going to follow the 150 watt described by the speedball instructions and yourself, but I see you mention a lightbox as an alternative. I have an A3 lightbox that I can borrow from work, that I think uses fluoresent strip lights: Do you think this would work, do you have any suggestions for timings, or is there a physical change with the emulsion when it has been sufficiently exposed that i should look for? Any advice would be appreciated and I'm looking forward to the results of my project!
Please us glass, not acrylic to press the positive against the stencil. Acrylics filter much more UV energy than glass, depending on the manufacturer. Us a piece of glass that is smaller than the inner dimension of the frame so the glass is not raised above the surface of the stencil and you will have much better intimate contact with the positive and the stencil.
aglaranna5 years ago
Should you turn off the main lights in whatever room you're working in? Or does that not tend to make much difference?

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