Using a 21-step Stouffer Wedge for photopolymer printmaking.
Care guidelines for the Stouffer Wedge
A Stouffer Wedge is a very handy tool to have in your studio especially if you are working in an artist printmaking studio, (as opposed to a professional commercial print shop).
A Stouffer Wedge is a strip of continuous tone film with a range of grey steps, with step 1 being clear film and step 21, 100% black. The numbers are clear so that you can see them on the processed plate. Your Stouffer Wedge measures the amount of UV output from your exposure unit lamps and is used to determine the correct amount of UV light needed to harden the photopolymer plate.
Light passes through the graded sections in greater or smaller amounts. Manufacturers of photopolymer plates suggest an ideal Stouffer Wedge reading for their particular type of plate. This reading is intended as a guide when exposing photopolymer plates to film that has been printed at a film lab on an imagesetter. An imagesetter is a high-resolution output device used in the commercial prepress printing industry that transfers electronic text and images to film. Imagesetters are becoming obsolete with the move to direct to plate processing.
Artists using a 21 step Stouffer Wedge for photopolymer plates
For artists making their own photopolymer plates in their studio, the optimum number or step on the Stouffer Wedge will be different, usually lower, depending on how you produce your film positive or film negative. Film produced through an inkjet or laser printer, or a drawing with pencils or pens on drafting film will not require the same number (usually 16) that is required for imagesetter film. Inkjet and laser printed films are not as opaque as imagesetter film, so a lower step (than the step recommended by the manufacturer) will be needed.
Experiment and make notes and refer back to your notes. Keep records of the following: Date, Job/Print, Plate Material, Lot#, Exposure time, Washout time, Washout temp, Drying time, Drying temp, Post-exposure time, Stouffer Wedge reading. By keeping this information you will be able to ensure that you are maintaining accurate records of your Stouffer Wedge and plate exposures. I also keep a technical notebook and write up exposure information on new projects as I am often making plates using very different film positives.
The intensity of your UV exposure unit, the type of film positive or film negative you use, and the type of photopolymer plate are all variations in getting an optimum exposure. You lengthen or shorten your exposure time to get your optimum exposure. Using a Stouffer Wedge on a spare strip of photopolymer plate alongside your exposed photopolymer plate will give you a step reading for future exposures (using the same UV exposure unit, film and photopolymer plate).
You can also use the Stouffer Wedge to ascertain the intensity of UV light when using a different or unfamiliar UV exposure unit. By testing the UV unit with a Stouffer Wedge you can see if the new unit is more or less powerful than the unit you have been using and adjust your exposure times accordingly. For example you may find that a 60 second exposure on your UV exposure unit works perfectly for a certain plate and particular film positive (inkjet or hand-drawn). Make a Stouffer Wedge exposure on the same plate for 60 seconds. Wash the plate to ascertain the step reading, which is the last step that has not washed away.
If you are having problems with your Stouffer Wedge exposure results, ensure that you are using UVA light bulbs or tubes, 360-400 nm (nanometers), and they are all working. If you are using sunlight, make plate exposures between 11am and 3pm when UV light is strongest. Your times will vary depending on your climate and the time of the year. When using sunlight to expose your plates you can do a test Stouffer Wedge exposure to get a reading of the intensity of the UV light on a test strip of your photopolymer plate. If you have previous results of working in sunlight, you can compare them.
You can use the Correction Table on the back of the Stouffer Wedge envelope to increase or decrease your exposure.
Care guidelines for the Stouffer Wedge
Caring for your 21-step Stouffer Wedge
- Keep the Stouffer Wedge safe, in its envelope. It’s very easy to lose!
- Handle the Stouffer Wedge with clean fingers, touching it only as necessary.
- Do not bend or crease the Stouffer Wedge.
- The Stouffer Wedge has a shiny side and a matte side. Place the matte side facing towards your photopolymer plate surface when exposing the plate. It is printed so that the numbers are right side up when you place the matte side on your plate surface.
- Use a strip of photopolymer plate slightly bigger than your Stouffer Wedge. Use only flat plate, with no bends or creases in it.
- If you are using imagesetter film (not inkjet or laser printed film) there will be a Stouffer Wedge reading that is recommended for the type of photopolymer plate you are using. Your commercial plate supplier can assist with this. (An art supply shop will not know.)
- If your Stouffer Wedge does get dirty, wipe it with a soft cloth and water if the dirt is water soluble. Try isopropyl alcohol or methylated spirits if the damp cloth does not remove the dirt.
- If you are careful with your Stouffer Wedge you should have many years service from it. After use, store it safely as soon as possible back in its envelope. If you work in a communal studio, write your name on the Stouffer Wedge envelope. A Stouffer Wedge does not usually get damaged, but it is very easy to lose.
Buy a Stouffer Wedge