Polyester plate lithography utilizes the repulsion between grease and water. Lithographic printing typically involves alternating between wetting the plate and rolling over it with oil based ink in multiple passes until the desired density of ink has built up. It is best to make a few proof prints on newsprint before starting an edition, or using expensive paper. A plate that undergoes repeated wiping, ink charging, and proof printing cycles becomes more ink loving and produces more consistent results.
Poly litho plates: a specific sheet polyester with open cells which fill with water, generally translucent & flexible like a sheet of fairly light weight paper. Note: it is important to work clean. Oily fingerprints & grease attract ink & show on your prints.
Drawing materials that hold oil based ink and are not water soluble: ball point pens, china markers and sharpies may be used to draw on the plate. Laser toner can painted on. You can also put the poly sheet through a laser copier to reproduce any image directly onto the plate.
Traditional oil based ink. Litho inks, etching & relief inks can be used. Inks may need to be amended for stiffness. Magnesium carbonate, stiffens ink. Burnt plate or flash oil will soften older very stiff ink. You need to have a fairly stiff, but workable ink. NOTE: water based, or water clean-up oil ink will not work!
- Gum arabic solution
- Citric acid powder
- Clean sponges
- Bowl for wetting solution
- Old phone books (or suitable cheap paper to drying your brayer between passes)
- Trays, if you will use wetting method #2, described below.
Making a Plate:
You can draw directly on the plate with various markers (see above) or paint onto the plate with acrylic medium, a solution of laser toner, or other materials. Many things work, and you can expreriment since plates are fairly cheap. Also you may be able to clean & reuse a plate. You may be able to scrape off unwanted drawing with a clean razor blade, but you may damage your plate.
- work clean & wash hands often: avoid oily smudging that will be hard to see and/or remove.
- mixing different materials on one plate makes consistent inking more difficult.
Heat set your plate before wetting & inking. A hairdryer works well for small plates or drawings: set the dryer on high and move the dryer very slowly over the image on the plate two or three times. Remember not to do this with the plate lyng on glass :-)!
Wetting Solution ( water, gum arabic solution, & citric acid):
Fill a quart size canning jar with room temperature or slightly tepid water, leaving about 2 inches of space at the top.
Add 1 oz of gum arabic solution & 1/2 teaspoon of citric acid powder, stir well, or shake to mix. Wait 1-2 minutes & mix again before using.
Wetting the Plate, Method 1:
1. Place the polyester plate on a clean, slightly wetted inking surface.
2. Dip a cellulose wiping sponge in the water, squeeze, and pass lightly over the plate a number of times.
Wetting the Plate, Method 2:
1. Place the polyester plate in a clean, flat tray. If you use a lightweight plastic tray or metal cookies sheet you may need to place a piece of of glass inside it to have a really flat surface.
2. Pour in wetting solution to just cover your plate.
The pores of the plate surface fill with water that repels the ink as you roll it on.
Lithographic Ink & Ink the Plate
Some litho inks are very stiff & hard, others are as malleable as etching ink. Use any oil based ink, except water clean up inks. Stiff inks are give the best detail reproduction; softer inks are easier to apply and give an image greater contrast. Oil-based etching inks are well-suited for printing polyester plates, but the ink may require the addition of a small amount of magnesium carbonate to stiffen it and to avoid scumming.
For a good black ink I recommend Graphic Chemical litho ink No 1921, which is ideal for the polyester plate process. Very stiff inks can be modified with linseed oil, flash oil, or burnt plate oil.
Whatever the consistency, the ink needs to be worked around with a spatula for a few minutes! Scrape the ink across a 10 x 10 inch surface and then use a good roller (preferably a softer nitrile roller) to roll out the ink evenly in a criss-cross pattern. A well rolled-out ink makes a smooth sort of hissing sound while charging.
- Dispense some litho ink onto your inking surface.
- Use a circular scraping action inside the can to dispense the ink, then cover the surface inside the tin with plastic film to prevent it drying out.
- Modify the ink as required.
- Work the ink for a few minutes.
- Gently start rolling over the dampened polyester plate – you may need to hold down the edge of the plate to prevent it from curling over the roller.
- After each inking you will need to dry your brayer on paper (old phone books work well!) before re-inking the brayer.
- Your plate needs to stay wet. If you are using the sponge wetting method , re-wet your plate after each roll-up, so the plate surface pores will remain ink-repellent.
It is rarely possible to charge a plate in one go. A well-charged plate usually requires the gentle and careful build up of successive layers of ink and water.
When a plate is freshly made, it may take from 4 to 10 ink and water cycles before it is fully charged with ink. However, once a plate has already printed, the surface becomes more ink loving and only a few inking-wiping cycles are needed to recharge.
Inking may leave smudges where they should not be: this is “scumming”. To remove scum from the plate, rinse with a solution of water and citric acid (no gum arabic): mix ½ tsp citric acid & 3 cups of water. To rinse, dribble a little solution over the scummed areas of your plate, then gently wipe with a clean damp sponge, avoiding the inked areas.
Note: if you get a lot of scumming, you may need to stiffen your ink (with magnesium carbonate) and/or dilute your wetting solution with a little more water to reduce the gum arabic ratio. If you use wetting method 2, replace your wetting bath with clean solution, & clean the tray as needed.
Polyester plates can be printed on a litho press, but many artists prefer using an etching press. To print a polyester lithograph it is crucial to use little or no felt material between the rollers to gain maximum contact between plate and paper. I use one thin blanket of vinyl interfacing, and full pressure.
- Gently peel the inked plate off the slab and place it onto your registration sheet.
- Lay the printing paper on top as though printing an etching.
- Lower the blanket and roll through the press.
For a quick proof with good registration you may try inversion printing: lay the damp paper on the press bed, flip the polyester plate face down and register the plate directly to the sheet of paper.
Cleaning the Plate
To clean the plate, run it through the press a few times with newsprint to absorb excess ink, then wipe it with concentrated dish soap solution. (TIP: Use a ratio of around 1 part dish soap to 10 parts water to obtain a strong detergent that is powerful enough to dissolve greasy ink residues.) Stubborn ink residues can be removed with toothpaste applied using a soft cloth. Clean the slab and rollers in successive stages using vegetable oil, baby oil, and detergent solution (in this order). Remember that, unlike VOCs, cleaning oils are non-volatile and act best if left to soak into the ink for a few minutes. Use a spatula to scrape off excess ink to save on cleaning rags.
To get good results in multi-plate multi-color printing it is particularly important to clean plates thoroughly after each printing stage, otherwise ink will be contaminated when recharging the plates. Use a three-step cleaning routine for each plate:
- Run off residual ink onto newsprint.
- De-scum the plate with wiping solution to remove ink offset from other plates.
- Dispense a blob of toothpaste onto a soft rag and use this to completely mop up any ink residues from the plate then clean and de-grease the plate with strong dish soap solution.
NOTE: use separate sponges & separate wiping bowls for each color to avoid contamination.
Paper for Poly Plate Lithographs
Lithographs can be printed on a wider variety of paper than etchings. Slightly textured rag paper can enhance the lithographic grainy look of the print. Smooth paper will provide clearer detail. Successful prints can be made on wet or dry paper. BFK Rives provides a good lightly textured surface. Arches 88 has a smoother surface.
If a print is too faint on dry paper, but the plate has been inked up correctly, using damp paper can rectify the problem. The result is a darker, crisp and clean image with more contrast than on dry paper.
To wet the paper dip each sheet in water then blot off the excess; you do not need to soak it. Many artists use the pronounced differences in printing on wet or dry paper to creative advantage: printing on dry gives a grainy very lithographic look, printing on wet gives a denser impression more like an etching.