The Stouffer Gauge: A Platemaking Pal

Whether you are processing photopolymer plates by hand in a DIY set-up or creating photopolymer plates with an industrial platemaking unit, the Stouffer 21-step Gauge is a commonly referred-to item and an invaluable tool to have in your platemaking arsenal.  The gauge will help you figure out the exposure times needed for your processing set-up and allow you to make calibrated, quality plates time and time again.

What is a Stouffer Gauge?

The Gauge itself is a small strip of reusable film negative that has numbers ranging from 1 to 21 corresponding to small blocks (or wedges) of tones ranging from light grey to a deep dark grey/black. The numbers are clear on the film allowing full light to pass through the film.

Like a normal piece of film, the Gauge had a dull side (emulsion) and shiny side (non-emulsion). For the gauge that we sell, the dull side (emulsion) shows the numbers in a wrong-reading orientation. The shiny side (non-emulsion) shows the number in a right-reading orientation.

When making plates, the dull side (emulsion) should face down and touch the plate.

How to Use The Stouffer Gauge

You’ll treat the gauge as a normal positive or negative film and process a small test plate. We recommend that you have a pad of paper & pen handy to record your test results and settings so that you can keep track of what times worked and which ones didn’t. If changing variables, change them one at at time and record your findings. This will keep your test (and results) organized and you can go back to previous tests if you have to backtrack.

recording-results

Before starting, make sure that your bulbs are at 100% and the correct type (UVA bulbs in the 360nm-400nm range – if using black light bulbs – confirm the range). If using the sun as a light source, you’ll need to choose a sunny day, preferably with no cloud coverage. Recommended timeframes are between 11 am – 3pm when the sun’s rays are at their strongest and highest in the sky.

Your goal is to achieve the manufacturer’s recommended Stouffer Scale range for that particular plate.

Place the Stouffer Gauge (emulsion side down) on a small square or rectangle scrap of unexposed photopolymer.

applygaugetounexposedsheet

If available, use the manufacturer’s recommended processing times as your starting point. If you need help with determining a good start time, contact us as we’d be more than happy to help out!

Expose per instructions for Main Exposure. You should see a faint outline of the stouffer scale when you hold the plate up and at an angle. Follow with Wash-out for the instructed time. If you are uncertain of the time for washout – check the plate at intervals to see if the edges of the exposure are clean and the plate doesn’t feel slippery or slimy. After rinsing the plate and sponging off extra moisture, you can check your Stouffer reading.

How to Read the Stouffer Gauge

To determine your exposure reading, read the lowest number of solid relief visible next to the clear exposed section of the Stouffer Gauge.

For example, the plate sample seen below has a recommended 16 on the gauge. The photo illustrates a good representation of the 16 wedge. The number (and corresponding wedge) is completely visible (e.g. not fattened, blotchy and not thinned out).

KF95 correctly exposed Stouffer Gauge test strip

Use the Correction Table (as marked on the back of the envelope that the Stouffer Gauge comes in) to increase or decrease your exposure if you need to.

exposure-correction-table-chart

Example: Using 40 watt UVA bulbs and aiming for a 16 on the Stouffer Gauge:

First trial’s main exposure time: 100 seconds resulted in a solid 15 (with the additional observed results of a blobby 16). A 15 is considered “underexposed” and too low.

Since we’re aiming for a solid 16, we’ll need to go up a step. Using the Exposure Correction Table, to go up a step (increase step guide by…) we need to take our original exposure (100 seconds) and multiply this by 1.4. The next recommended exposure time is then 140 seconds.

Example: Using a single Nu-Arc UVA bulb and aiming for a 16 on the Stouffer Gauge:

First trial’s main exposure time: 600 seconds resulted in a solid 17 (with blobby edges around the top of the 17). A 17 is considered “overexposed” and the exposure time is too high/much.

As we’re aiming for a solid 16, we’ll need to go down a step. Using the Exposure Correction Table, to down a step (decrease step guide by…) we need to take our original exposure (600 seconds) and multiply this by 0.7. The next recommended exposure time is then 420 seconds.

Troubleshooting

Why are my numbers wrong reading when I’m looking at the fully processed plate?

The film strip was incorrectly applied (it was flipped) when placed on the unexposed plate. For the 21-Step Stouffer Gauge, the emulsion side should be face down and be touch the emulsion side of the unexposed photopolymer. If looking down at your set-up, you should be able to see the number and text in a right-reading format.

My target number is blobby or washed out What’s happening?

If your wash-out and dry times are correct, then you are underexposing your film. But you are almost there to your ideal exposure time. This means that the photopolymer hasn’t been hardened up enough to be able to hold on the plate when your plate is being washed and dried. Try boosting up your exposure time by 1/2 a step. This is where keeping track of your test times will be important. You are narrowing in on the time.

underexposed

All of my number and tones are completely hardened up and I can’t see anything at all. What gives?

If your wash-out and dry times are correct, then you are overexposing your film by a bit. This means that all of the photopolymer has hardened up beyond what you need and is running into the risk of being over-exposed and flaking off. Try shortening your exposure time.

overexposed

I’m recording a really, really long exposure time ( about 10 minutes + ). What’s going on?

A likely suspect is that something that is affecting your light source. Common issues are:

  • Bulbs are low wattage (e.g. 15watt): A low bulb emitting a low wattage of light will take much longer to harden the plate as compared to a higher wattage bulb (e.g. 40watt). Some platemaking units were not designed to hold higher wattage bulbs. Also consult your platemakers recommended bulb specifications to avoid malfunctions.
  • Bulbs are not outputting at full capacity: Bulbs should be changed if they fall below 70% output.  Longer and increased exposure times from your optimal time are a sign of diminishing output.  We suggest changing them out for new bulbs as this will give you the most accurate results (Boxcar Press can provide you with new light bulbs). You will need to run a new stouffer test every time you replace your light bulbs.
  • Bulbs are too far from your plates or there are not enough of them or close enough together. Bulbs work best at 1.5” – 3” max away from your plate. Multiple bulbs next to each other give the best results for good plates as the light comes from both the sides and top to create strong relief on the plate. Your exposure unit may need some re-configuration.
  • Using the sun: the sun’s rays will not be uniform in strength or duration as ozone, potential cloud coverages, and other spatial interferences will make the light emission vary in intensity. As powerful an energy source the sun is… it fluctuates and will take a lot longer to expose a plate properly as compared to an industrial exposure unit with calibrated bulbs. But it’s free and plentiful and a long exposure time may be what it takes.  This is where your Stouffer scale reading will guide you.

I’m using a Nu-Arc. Any tips?

The Nu-Arc unit measures in light units and typically only has one bulb that is farther away from the plate.  Times for exposure will be longer because of this light source.   You will have to rely heavily on your Stouffer Gauge for pinpointing your time.  If you have a large model, you may not be able to make a plate as large as the glass frame.  The exposure times at the edges of the machine may be different than your center.  A stouffer test at the center and corners will help determine that.

For more helpful tips on the DIY platemaking process and set-up, letterpresscommons.com has a plethora of information to check out here.

One Last Dance For Photopolymer Plates: Ink Stamp Pads

Here at Boxcar Press we’re always looking for new ways to give printing supplies “one last dance” before recycling or dismissing items into the wastebasket. One of our clever and resourceful platemaking customers, Meredith Pinson-Creasey of Purple Dog Press shares with us an experimental & last-time use for her custom-ordered photopolymer plates: using ink stamp pads to apply ink to the plates. Meredith weighs in on the pros and cons of using ink stamp pads for printing (and with some rather nice results).

Helpful note: please do remember that our custom-made photopolymer plates work best with letterpress printing inks (such as rubber-based or oil-based inks) which are rolled on to the surface of the plate.  Many other art inks are water-based and since our plates are water-wash out, using these products can degrade the quality of plates. Please use caution and good judgement if experimenting with water-based ink stamp products.

THE EXPERIMENTAL PROJECT I have been experimenting with some of my old polymer plates, trying to get my logo to print on the cotton twill fabric tape and boxes I use to wrap my letterpress cards for gifting. You guys may have already tried this and I may not be sharing new info, but I’ve had great luck.

My 82 year old mother continues to be the most fearless artist and crafter I know. And her father could repair or make just about anything. It is their “eat first, ask questions later” attitudes that inspire me. As a sports, landscape, and baby photographer, and an amateur letterpress printer with a 1940’s 10 x 15 Kluge, I wanted the packaging for my photo/letterpress cards to be personalized with both my logo and the recipient’s name, or a greeting. The most economical route was to purchase blank ribbon, boxes, and bags to customize as needed. I have printed my own packaging using silkscreen and linoleum blocks, but wanted something faster with less set up time. Having dozens of rubber stamps made was too expensive. So I decided to experiment with some of my retired polymer plates from Boxcar Press.

Using photopolymer plates experimentally with ink stamp pads for a final use.

INK PAD TIPS Working with dye or solvent ink pads produced the crispest image, due in large part to the firm surface of the pad. Pigment inks have a foam pad which can cause the ink to go down into the recessed portions of the polymer plate producing a blurred image. A brayer may also be used to transfer the ink from the pad to the polymer plate to provide even coverage and less mess.

Using polymer plates as a stamp works best when attached to a block of wood or a clear stamping block to ensure only the image or text comes in contact with the fabric. The wood block I used has a slick finish designed to release the temporary stamp easily. Three brands of ink pads worked well for me: Ranger Ink; Hero Arts; and StazOn. Ranger Ink’s “Dye Ink Pad” and “Archival Ink” in all colors I tried worked well. Hero Arts makes terrific “Neon Dye” Ink colors. StazOn’s “Solvent Ink Pad” worked equally well. These inks are waterproof, permanent, acid-free. and the pads are refillable. My guess is that most brands of dye or solvent ink would produce great results.

Using photopolymer plates experimentally with ink stamp pads for a final use.

MATERIALS TO TRY (AND ONES TO AVOID) A few of the materials I’ve stamped with polymer plates include: birch wood tags, twill ribbon tape, glassine food bags, kraft gift boxes, and paper. Although pleased with all the results, the glassine takes FOREVER to dry and the wood tends to bleed sometimes. The bleed may be the result of over inking or applying too much pressure to the stamp because some of the images did not bleed. Kraft paper enhanced the grunge look of one of the fonts. Ink wipes off easily easily with a cloth but will stain the recessed portion of the plate.

(Boxcar’s note: One important thing to note about polymer plates versus rubber stamps which can affect your results and determine which materials are best to stamp on. A polymer plate is a hard surface on a thin substrate. In contrast, a rubber stamp is soft, pliable and cushiony. These properties will work for or against you when you are stamping and experimenting will be key).

THE RESULTS Text of various sizes and weights, and line drawings as thin as .75pt printed well. Because the inks are translucent, this alternative use of polymer plates will not produce a silkscreen type effect.  My faux postage cancellation polymer plates worked great and the uneven application of ink makes it look even more authentic. Expect to see the fabric beneath graphics containing large areas of solid polymer. For best results, I recommend using plates no larger than about 4 x 6 inches, or about the size of your hand.

Using photopolymer plates experimentally with ink stamp pads for a final use.

I love it when my tools can do double duty and this is much more economical than having dozens of custom rubber stamps made. Now if I could get my Kluge to churn butter or something, maybe my husband wouldn’t grumble about the space it requires.

WHAT’S NEXT No longer limited to someone else’s rubber stamp designs, I am looking forward to putting some of my own quotes and graphics in polymer. When I gang up those plates for my Kluge, I’ll be squeezing in another stamp idea. While this alternative use of polymer plates may not appeal to a commercial print shop, I do recommend the idea to anyone looking to complete their branding with a personal handmade touch.

THE FINE PRINT So here’s the fine print: polymer plates degrade with water. Rubber stamp inks are water based. Polymer plates don’t really play well with rubber stamp ink and will degrade over time. I think I’ll go through quite a bit of ribbon before that happens, but I’ll keep my stamping plates separate from my printing plates.

A huge appreciative round of thanks goes out Meredith of Purple Dog Press for her excellent advice and tips!