Polyester Plate Lithography / Pronto Plates

Kevin Haas | www.wsu.edu/~khaas

CREATING YOUR IMAGE
DRAWING MATERIALS Ball Point Pen, Sharpie or Permanent Marker, China Marker/ Litho Crayons, Photocopier Toner (Must be heat-set in an oven or on a hot plate at 225º – 250º for 10 minutes.)

PHOTOCOPIED AND DIGITAL IMAGES
Using Adobe Photoshop and a laser printer you can easily scan and print images onto polyester plates. A 1200dpi laser printer such as an HP 5000, a GCC Elite XL or a Xante printer will work best. However, it is best to make a few adjustments to your print settings to make polyester plates print easily and accurately at the press. By default most laser printers will print images over 133 lines per inch. Lines per inch (lpi) is a measurement of how many lines of small varying sized halftone dots are used to create the illusion of a continuous tone image. Since printing these plates by hand requires more ink and pressure than offset printing, which is what these plates were intended for, we need to decrease the lpi to 75. If you did not do this, the ink sitting on top of all the very tiny halftone dots would likely run together, or ‘bridge’. To prevent this from happening, lower the lpi to maintain a balance between the amount of ink that is needed to print and the space around the dots to hold water that repels the ink. As you gain more control over your printing the easier it will be for you to print higher lpi images. 95lpi is fine for hand printing, but can still be manageable. Another good thing to keep in mind is the size of your image. Although the plate size may be 11×17” or 13×19”, it can be difficult to ink an image that covers almost the entire plate. I would recommend at least 1” margins on each side and printing no larger than an 9×15 image on an 11×17” plate, and a 11×17” image on a 13×19” plate. These are the steps you should follow to properly image your polyester plates:

  1. Check your Page Setup. MB > File > Page Setup…
    Set the Format to the printer you are using and the Page Size to match the size of the polyester plates. Orientation (portrait or landscape) should also be set at this time.

  2. Set your Printing Options MB > File > Print with Preview…
    Use this dialogue box to flip the image so it will be backwards on the plate by checking the ‘Emulsion Down’ box. This is also where you will access the Screen settings to change the lpi of the printed image. Set your Halftone Screen’s Lines Per Inch to 75. Angles for 4 Color images: Black/Darkest Color: 45°, Cyan/Next Lighter: 15°, Magenta/Next Lighter: 75°, Yellow/Lightest: 90°.

  3. Set the image Quality Settings MB > File > Print

  4. Load your polyester plate into the manual feed tray on the printer and click Print. Viola!

PRINTING YOUR PLATES
MATERIALS
• Printing Paper, Newsprint
• Two Bowls one filled with 1 L water and 30ml Gum Arabic
• One large sponge cut in half
• Felt & Toothpaste
• Inking Brayers
• Lithography Inks: Black(Graphic #1796), Handschy Yellow, Magenta, Cyan, White, Tint Base/Transparent Base
• Magnesium Carbonate or #8 Varnish.

GENERAL SETUP
Prepare newsprint, and printing paper, making sure to add the ‘T’ and Bar registration marks on the back of the paper. Mix and modify your inks as needed and roll out your slab of ink with the brayer. Fill one bowl with about 1L water and 15ml of Gum Arabic. This will help reduce the Ph of the water. Ideally, polyester plates work best with a dampening solution between 5.5 and 4.5 Ph, but I find that the small amount of Gum Arabic in the water is adequate. Rinse your sponges. Setup the press, checking pressure, and registration on your plates.

MIXING AND MODIFYING INKS
Polyester plates print best with inks that are moderately stiff with a fair bit of length. True lithographic inks for hand printing are very stiff and moderately short. An ink such as Daniel Smith’s Crayon Black is too stiff for polyester plates and should be modified by adding a lighter varnish, such as #3, or by adding Handschy CS800 transparent base to make it more pliable for printing these plates. The Graphic Chemical Litho Black #1796 works well, but may need a small amount of mag or #8 varnish. Color Litho inks, such as the Handschy line of inks, may work well out of the can but will often need to be modified with Magnesium Carbonate. Slowly fold it into your ink until it is mixed in well and then check the consistency to determine if it is correct. It should hold its shape as it sits on the slab rather than immediately relaxing into a blob. If the pigment ‘bleeds’ from your ink while printing, such as it will do with magenta and cyan, adding #8 varnish or body gum to the ink will help greatly. Color mixtures using mostly Handschy Tint Base will require more mag.

PRESS SETUP
Printing using an etching press
To print on the Brand etching press, set the pressure to –1|0, so the roller is just in contact with the press bed. It is easiest to ink your plate on a separate glass slab before printing. Once it is inked, place the dried plate face up on the center of the bed and your paper face down on the plate. Cover the plate and paper with 2 sheets of newsprint. Place a tympan on top and run them through the press. Felts are not needed.

Printing using a litho press
To print on a litho press, lay your plate centered and face up on the press. Place your paper on the plate according to your registration marks, and cover with two sheets of newsprint. Cover with a greased tympan and print. You should only use as much pressure as needed to pull a good impression. The plate will break down quicker if excessive pressure is used. Before you print, set up the litho press by centering your plate, setting the pressure, and marking your start and stop points (traverse marks).