In August '62 I started doing silkscreens. I wanted something stronger that gave more of an assembly line effect. With silkscreening you pick a photograph, blow it up, transfer it in glue onto silk, and then roll ink across it so the ink goes through the silk but not through the glue. That way you get the same image, slightly different each time. It was all so simple quick and chancy. I was thrilled with it. When Marilyn Monroe happened to die that month, I got the idea to make screens of her beautiful face the first Marilyns.From that description I surmised that I would need to forge an image into glue applied to a screen. After laying the forged screen on paper or fabric, ink would be pushed through the forged image only, connecting with the paper or fabric below it. There are other options - the fastest, least expensive, and simplest being to use (freezer) paper stencils - but I want the Warhol way so I researched and came up with this procedure.
- Preparing a UV-Free Space
- Assembling an Exposure Unit
- Getting a Screen Drying Rack
- Creating the Artwork
- Outputting the Screen Positive
- Emulsifying the Screen
- Exposing the Screen Positive on the Emulsified Screen
- Printing With Your Screen
- Curing Your Print
- Checking Up
Preparing a UV-Free SpaceA number of steps in the screen printing process involves work that needs to be done in a room where no ultraviolet light is allowed to enter. This UV-free space is where you'll work with chemical emulsion which is sensitive to UV rays. There needs to be some square footage available as you will be emulsifying your screens, exposing your artwork to the emulsified screens, and storing emulsified screens for future use. You will also need space for an exposure unit and screen drying rack. Ideally, this space might be near a washout area and garden hose (with a high pressure setting) to wash out the unexposed emulsifier or reclaim/reuse/clean your screens. This UV-free space can be created in a small room or shack. First use Rubylith Masking Film to cover up all areas where natural UV rays from the sun or other light source might be able to enter the room. This includes windows or cracks between paneling. Now, swap out all the bulbs in your space to bug lights - yellow incandescent bulbs that can be bought in any hardware store. Lastly, you can hang a black cloth that, similar to a shower curtain, can pull across a closed door if light enters through the door jamb.
Assembling an Exposure UnitI couldn't explain it any better than Bob Mongiello. This unit must fit in your UV-free space.
- 500 Watt Halogen Work Light ($9) should come with small stand, on/off switch, remove the glass from Halogen light because the glass might have a UV filter in it and you don't want a UV filter
- Stand - [a] 3/4 inch 24 x 20 plywood for base [b] cut a 2 x 4 to attach, this will hold the light [c] attach 2 x 4 with screws to base [d] attach 20 inch support 2 x 4 from base to stand
- Use another 20 inch 2 x 4 with a screwed in piece of plywood to hold stand of the Halogen light, attach this to the top of stand, plywood is extra long to allow for adjustments with screen size
- Attach shelf to hold the screen while you are burning it - shelf is 30 x 24 and must be painted black so no light is reflected back
- Distance between the light and screen (laying on shelf) should be 12 inches
- Brace shelf with wood support as you braced the stand
- Don't touch the Halogen light bulb with your hands
- Get a 15 x 17 inch piece of commercial glass (with no UV filter) to hold the film positive to the screen while exposing - 1/4 inch thick, edges sanded with sandpaper - no picture frame glass
Getting a Screen Drying RackGet or build a drying rack to dry screens after prepping them for emulsion or coating with emulsion. You can also build something on the wall of your UV-free space as this unit must fit in your UV-free space.
Creating the ArtworkThe artwork can be created in a vector or bitmap application like Illustrator and Photoshop, respectively. I'll be working with simple one color vector or bitmap images. Artwork with multiple colors needs to be separated - each CMYK color is pulled out from the original image and output in black separately. For printing, the separate screen positives are burned to individual screens. The screens must then be lined up exactly for the complete image to emerge correctly. The base of the press should have pins or an edge that helps to line up each screen; registration marks on the image output is also helpful. (It might be better to use the single station table top press with four screen clamps when printing color separations on one piece of paper or fabric.)
Outputting the Screen PositiveAfter your artwork is created and/or separated, you will need to convert it to all black and produce what are known as screen positives. A screen positive is any opaque image of (usually) black ink on any transparent or translucent surface (acetate, vellum or transparency). (If your art has more than one color, you will need a film positive for each different color.) You can use most standard printers to output a screen positive, or outsource the work to a copy shop like Kinko's. (Are Kinko's still around?) You may also use a copy machine but in order to satisfactorily produce a screen positive using a copy machine, the black and white line work must be opaque and a photographic print must have high contrast.
Emulsifying the Screen
- Presensitized emulsion is premixed, lasts about a year, exposure time must be exact or the emulsion will not harden correctly
- Unsensitized (dual care) emulsion requires mixing with sensitizer, lasts about three months, can under or over expose and still good, recommended for beginners
Exposing the Screen Positive on the Emulsified ScreenA screen positive transparency is taped to a tightly meshed screen which has been coated and dried with emulsion. When exposed to light emitting UV rays, this emulsion turns hard. The black ink on the transparency prevents light from hardening the emulsion where the black ink covers it. To expose the screen positive, use the exposure unit in the UV-free space. Place the screen positive on the emulsified screen. Be sure the graphic has the correct placement / orientation and affix the screen positive to the emulsion coated screen with clear Scotch tape. Place a 15 x 17 inch piece of commercial glass on top of the screen positive to hold it in place. (Always make sure the exposure glass is clean.) The hardening time of the exposed emulsion varies based on the type of emulsion and light source intensity so we'll generalize at 3-10 minutes. After exposure, take the screen to a wash tub where the unhardened portions of the emulsion (what was under the ink during exposure) can be blown out with a high pressure water hose. Remember you still can't expose the unhardened portions of the screen to UV rays. Apply a forceful spray of water (body temperature) to both sides of the screen. DO NOT USE HOT WATER. Concentrate this spray on the top side of the screen. After a few minutes, these areas will open. Continue spraying until all unwanted emulsion is gone. Once you have completely washed the screen, let it dry thoroughly in a level flat position. Hold the dry frame to the light and check for pin holes. (These can be covered.) There is now a stencil on the screen that can be used to print.
Printing with Your ScreenFor this process, I figured I would need a rather large table with clamps to hold the paper or fabric taut, or one of the following table top presses with one screen clamp for one screen. single station table top press with four screen clamps for color separations is also available. You can use Plastisol inks or water-based inks. If you are using Plastisol (recommended for longer lasting graphics), you will need some sort of dryer either a flash unit with heat control box or a conveyor dryer to either flash cure between colors or cure one color prints. Some have had success with a heat gun to flash dry the print and a heat press to cure the ink. If you use water-based you can probably get by with a hand held heat gun with a one station four color press although it is definitely not the most effective way to dry but an option. The type of ink used in screen printing depends on the type of printed object. The opacity of the ink is also an important consideration. Simple, one color designs may require opaque ink to really stand out. But it's just as important for other inks to be translucent. Just four colors--cyan, yellow, magenta and black--when properly layered, blend to create every color of the rainbow. Squeegees push the ink through your stencil on the mesh and onto the shirt or paper. The squeegee should be as wide as the interior of the frame. The squeegee pushes the ink, it doesn't spread the ink. This means that the squeegee should be held at an almost 90° angle to the screen. Important notes for printing with fabric inks:
- Usually two (2) people should work on the printing process – one holding the screen frame tightly against the fabric, and the other doing the printing.
- On articles like T-shirts, a piece of foamcore, cardboard or paper must be put inside each garment to act as a barrier.
- To improve the lubricity (slipperiness) of the ink, you may add the Transparent Base. To slow drying or to prevent screen clogging, add the Retarder Base (1-2 tbs. to 8 oz. of ink).
- Wash-up of screens and tools must be done immediately after use. If they are allowed to dry on your screen or tools, they are difficult or impossible to remove.
- After the fabric ink dries on the fabric, set a household iron at the highest dry heat (no steam) that will not scorch the fabric and with a cloth or paper between the iron and printed material, iron on each side for 3 – 5 minutes. This will make the ink withstand repeated washings.
- Use only fabrics that can be subjected to temperatures of at least 275 - 375° F. Do not use on non-porous fabrics such as nylon.
- Pre-test all fabrics. Fabrics with sizing must be washed prior to printing to assure proper adhesion of the fabric ink to the fabric.
- If inadequate wash fastness occurs, the print needs to be heat set longer.
- Put screen wash on a paper towel and use it to take ink off your screen.
Curing Your Print
from this excellent article on curing.
A flash cure unit is intended for flash curing (getting only the surface layer of the ink up to 320°) before applying a second print stroke to achieve opacity. With the right ink, you can flash cure a print in 7-10 seconds. To completely cure a print with a flash cure unit, you will need to expose it for 35-45 seconds. If you are going to use a flash cure unit to do the final cure of your items, you should invest (about $80) in a non-contact temp gun with laser pointer. If you're printing with Plastisol, most Plastisol cures at about 320°F. (Clothes come out of the dryer at about 500°F. Overcuring will result in a print that will crack and fade prematurely.) Be sure the Plastisol reaches the cure temp all the way through to be fully cured. Also, you should use something other than your printing platen to place the item upon that you wish to fully cure because the platens are not designed to handle that much heat constantly. When flashing Plastisol (as in a print-flash-print operation), you only want to "gel" the surface of the Plastisol which will usually occur at about 270°F. Much lower than the temps you'll see of about 350-400°F needed to insure the Plastisol has completely reached the necessary fully-cured stage. Some things to note:
- Some cure the print on the outside first and then turn it inside out to heat the inside of the shirt and ensure the Plastisol is fully cured.
- Infrared, quartz and hallogen flash units are available. Quartz is choice since the bulb technology delivers a much more uniform heat across the print.
- When a flash cure unit is operating, it reaches a temperature of around 600°.
- Always let your flash cure unit warm up prior to beginning production. Even if it has a temperature read-out, it is still a good idea to let the unit warm up. A 15-20 minute warm-up is usually sufficient. However, if in doubt, it's not a bad idea to check the temperature with a temperature heat gun. (See below.)
- Some flash cure units do not come with an on/off light.
- Never touch the heating element on the unit to see if it's on.
- Never leave the unit hovering over anything when it is on.
- Keep a record of dryer settings, temperature settings, notes about inks, and other important details that are specific to your printing equipment and capabilities.
- A flash will cure water-based ink fine. Just pull the print away from the platten as you want the water to evaporate away. Set the flash a bit further away than you do with Plastisol and flash. You should get steam as the heat dries the water out. Water-based inks take a much longer time to dry/cure than Plastisol. Generally about 2 minutes.
- The fabric type and color affect the curing time. Dark colored shirts will cure faster than white and light colored shirts. White, cotton shirts will take longer to cure than black (or other dark) 50/50 blend shirts.
- Temperature tapes are little strips of specially made paper printed with temperature readings that will indicate the temperature as a garment is being cured. These paper thermometers were the standard way to test temperature for years and are still used. Although they are only accurate within 15 degrees (if you are lucky), they are the least expensive and close enough item we have. If you can get one to turn black at around 330 degrees, then you know you are probably running AT LEAST 300 degrees based on the heater height and temperature. Temperature strips are inexpensive and available at most screen printing supply vendors; you can cut them in half so the cost per unit is even less.
- A non contact pyrometer is a useful device for checking the temperature of the print when being flashed. Simply point the gun at the ink when the garment leaves the dryer and it will read the surface temperature of the ink. While the pyrometer does not give the final word that a shirt is completely cured, it is useful for measuring temperature and providing a reasonable assurance that the shirts are curing properly.
- Stretching the print on the shirt to see if it cracks has a limited value for checking for curing of the print. The idea behind this test is if the print cracks during stretching it is most likely under cured. It is suggested using this test for spot checking only.
- The only guaranteed way to determine if your prints are curing properly is to do a wash test. It is a good habit to periodically wash a test shirt to see if your dryer is working as expected. What can you tell from the wash test? If the print was only partially cured, some or most of the print would have washed off. If the print was severely undercured, the print will most likely be completely gone.
Checking UpIn addition to the tools mentioned, you might benefit from the following.
- Ink solvents to clean up ink and clean screens or tools used to handle inks
- Chemical resistant spray bottles for screen making chemicals
- Ink scoops or spatulas to get ink form the bucket to the screen and back again.
- Ruler and t square for marking pallets with a Sharpie and aligning film on screens.
- Masking tape or screen tape to block off the sides of the screen or unwanted portions of stencil on the screen
- Spot cleaning gun for removing unwanted spots of cured plastisol ink from printed shirts.
- Inkjet or laser film for making your film positives from your artwork
- Spot cleaning fluid for the spot cleaning gun
- Scorch out to remove yellowing from white shirts that turn yellowish from excessive heat