Platemaking by hand is a straightforward process. Photopolymer plates have a light-sensitive surface on either plastic backing or metal backing. A film negative is placed over the plate surface, secured with Kreene or a glass covering, and exposed to ultraviolet light. Where the light hits the plate, the plate is exposed and hardened. What isn’t exposed because it’s blocked by the black part of the film negative will be washed out by water; what is is exposed to the uv light hardens and will not wash away, leaving a relief surface from which to print. Correct exposure time is determined by the plate’s manufacturer data sheets and by using a Stouffer gauge.
Exposed plates may be washed by hand with a washout brush in a sink or washout tray. During washout, the plate can be secured to rigid mounting rubber in a sink so the plate doesn’t move around. Washout brushes are very soft and supple. Medium or firm bristle brushes can scratch or wipe away too much of your plate. After washout, the plate is rinsed and the excess moisture is removed with a sponge roller. The plate is dried at a low heat temperature. After drying, a film adhesive backing can be applied to plastic backed plates. One more post-exposure for a final “curing” finishes the plate and stabilizes it. If you are using a platemaker or a washout unit, a magnetic mounting rubber may be attached to the top of a platemakers unit to hold both metal or plastic backed plates. Green die sealer is helpful for maintaining the seal of mounting rubber to the plastic or metal backing.
Making Your Own Plates: What You Need
Are you a do-it-yourself platemaker who wants to try and master the process in your own workspace? Here are the requirements for materials needed for exposing your own plates, including some other options if you want to experiment with some more primitive equipment:
UV Exposure Element
UV light bulbs (think tanning) usually work best in a light box. You can control your exposure times using bulbs that will give consistent results for each exposure. Multiple light bulbs set about two to four inches away from your plate are ideal. A good plate with firm shoulders needs the light from multiple sides; here are some guidelines based on your project:
- Projects measuring up to 10” x 13:” minimum of six (6) 25 watt bulbs spaced next to each other.
- Projects measuring up to 12” x 18:” minimum of ten (10) 40 watt bulbs spaced next to each other.
- Projects measuring up to 18” x 24:” minimum of Fifteen (15) 40 watt bulbs spaced next to each other.
If you can’t find tanning bulbs, than black light bulbs are an alternative. Other options for UV light source: the good old sun. This is a untested source and will need a lot of patience and experimentation.
Service Bureaus: Film Negatives
Though they are dwindling in numbers, there are still companies called Printing Service Bureaus that will process film for you. They are also called Digital imaging centers or Prepress Shops. You will want to order Right Reading Emulsion Side Up film or RREU. The film will have a shiny side and a dull side. The dull side is placed against your polymer plate. Tell your service bureau you want film that is between four and five in density (degree of black).
You may also use transparencies printed with a desktop printer. The challenge with that is that desktop printers can’t achieve the density of black that a film can. Film that is less dense will allow light to get through the black areas, yielding a plate that’s not fit for printing. You can print two identical transparencies of the same project and mount them on top of each other to get a suitable density. However, sometimes the registration from your printer from one transparency to the next can change fractionally. This method might not yield fine details or lines.
After exposure, the plates are washed out with water. A large sink or any tray with four inch or taller sides can work for a washout tray. The temperature of your washout water should be approximately 74 degrees F (24 degrees C). Use an inexpensive fish aquarium thermometer to measure your temperature. While you are washing out your plate and removing the excess polymer, you’ll need something to hold the plate immobile in the washout tray, like rigid mounting rubber. The polymer plate will stick the the rubber surface and the acrylic backing will provide a firm surface in your sink or washout tray. Both metal and plastic backed plates will hold to the rubber. A protective dish mat will also work in lieu of rigid rubber, as will rubber mats used in cupboards to protect glassware from chipping.
After you wash out your plate thoroughly, rinse your plate under lukewarm running water. Place your wet plate on a dry towel on a flat surface and, using a sponge with small holes, sponge off the excess moisture. The smaller the holes of the sponge, the better you can get moisture off. Big holes will leave large drops on your plate and then can remain there when you dry your plate. Car wash sponges are good for this.
Heat Drying System
Your plate will need to dry for 10-13 minutes depending on the plate type. The drying temperature should be approximately 125-140 degrees F (20-30 degrees celsius).
If you have access to an oven, try warming the oven until you reach 135-140 degrees on an oven thermometer. Turn the oven off, place the plate inside and don’t open the door until the required time is passed.
Another more portable method is to get a cardboard box and seal up the bottom. Turn the box over and carve out a hole large enough for a blow dryer nozzle. Put the nozzle through the hole, run the hair dryer for the desired time. Keep the box upside down so no air escapes and you keep the heat inside. Be careful not to block the vents of the hair dryer.
Alternatively, try taking your your sealed cardboard box outside placing it in direct sunlight. Lay the plate down and the box over it to protect it from the sun’s rays. The box should warm up enough to dry the plate.
Storage for Unexposed Plates
Store unexposed plates in protective black photographic bags. Use these bags for long term storage. Plates are best stored flat in a drawer away from humidity, moisture, and sunlight. Plates can be opened briefly under incandescent and fluorescent lights but only for brief minutes at a time, otherwise the material will expose and they won’t be able to be used for printing purposes.
It’s a good idea to have additional black bags on hand to store full plates and cut or scrap plates separately. Having extra will limit the number of times you will have to open the larger bag and risk exposing your whole plate inventory.
- Printmaking Centers Teaching Platemaking
- McClain Printing (for UV light boxes)
- Boxcar Press (for all manner of plates and platemaking supplies)