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Unexposed Photopolymer

How are plastic-backed and steel-backed plates different?

When mounted on their appropriate bases, plastic-backed and steel-backed photopolymer plates both create type-high surfaces for letterpress printing. Both plate types are recyclable. We’ll talk about some of their differences below.

Plastic-backed polymer plates are flexible, transparent, easy to cut, and mount onto a Boxcar Base for simple registration. You’ll find these plates:

  • can be cut with scissors in both their unexposed and exposed forms.
  • are transparent, meaning you can see the Boxcar Base’s grid through your plate. This allows for simple alignment of your plates to your base: For perfect registration, align a certain element of your plate to the grid: take a horizontal or vertical element in your plate (this could be your registration marks, or a horizontal line in your artwork) and line it up to the grid.
  • eliminate plate creep (steel-backed plate users sometimes experience this while on press). The plastic-backed plate’s adhesive is shift resistant, giving you a secure, strong hold during printing (but the adhesive also peels up easily when you’re done printing)
  • allow printers to print two color jobs using one plate if the design elements don’t touch. Cut out the second color images/text with a craft knife or scissors and set aside. Print color #1. Set your second color images back in place and pull up the first plate for color #1—perfect registration!
  • allow designs to be ganged up on plates closely to save space (and money).
  • are reusable. You will be able to reuse the plate many times if you keep the adhesive protected with the blue overlay after printing.  You can also replace adhesive for even more extended plate use.
  • more prone to curling, especially with large solid areas over time.
  • If purchasing unexposed plastic-backed polymer plates, you’ll also want to purchase film adhesive to adhere your plates to your base. If we’re making your plates for you, we include adhesive.
  • are suitable for metal clay jewelry.
  • Over here at Boxcar, we use plastic-backed plates for all our printing (the Jet 94 Clear plate paired with the Standard Boxcar Base).

Steel-backed polymer plates are compatible with magnetic bases, generally the Patmag or Bunting base. Steel-backed polymer plates:

  • require cutting with a metal shear or heavy-duty trimmer. You can use tin snips, though you may end up with kinks in your plate, as tin snips won’t cut as cleanly.
  • sometimes shift and creep on your base during printing. Magnets in the base effectively hold a plate from peeling but cannot always hold a plate from moving side to side. The cylinder or rollers of a press can move steel-backed plates out of register (that’s “plate creep”).
  • are not transparent. Because magnetic bases aren’t gridded (and you can’t see through these plates),  you’ll have to align your plates to your base with a line gauge and possibly registration marks. This works, but it is more time consuming and there’s more room for error.
  • are rigid, meaning they don’t bend well. This inflexibility can cause plates to kink and warp when handled so that their corners may work up while on press. Steel-backed plates are, however, very durable and not prone to curling over time.
  • can be more expensive than plastic-backed plates because you may require registration or crop marks which makes for a larger plate.
  • are difficult to get on and off the base, especially when the base has inlaid magnets. When placing metal plates on a magnetic base, keep fingers clear so they don’t get pinched when the magnet grabs. When taking your plate off the base, try an ink knife to pry under the plates to release from the magnetic base.
  • have sharp edges, which dictate extra care when handling.
  • can be used for a wide range of printing and impression—on leather, metal clay jewelry, ultra heavy-weight paper stocks. Steel-backed plates can also be used on etching presses when relief printing is desired. They are not suitable for high temperatures of foil stamping though.

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I want to use photopolymer to do something other than letterpress printing. How do I know what plate to use?

While our troubleshooting only extends to using photopolymer plates for letterpress printing, there are literally dozens of other uses for photopolymer plates. If you know the tech specs of the plate that you need, or if you can send us a sample of the plate required for your application, we would be happy to try and recommend a plate that we have in stock that will work for you.

We have innovative people using our plates for metal clay jewelry making, translucent porcelain, and leather work. We always like to hear what you want to try.

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Is processing a photopolymer plate toxic?

None of the byproducts of processing photopolymer plates are known to have health risks, except if you’re allergic by contact to plastic. Check out the MSDS’s for more specific health information. You can find each plate’s MSDS on it’s product page: plastic-backed plates; steel-backed plates; intaglio plates.

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I’m a metal clay artist. What photopolymer plates do I use?

We carry plates that are very similar to those recommended by Art Jewelry Magazine. Many metal clay artists have used our plates to great success. We have several plate types that will suit your needs and preferences.

What Boxcar photopolymer should you use for metal clay?
Art Jewelry Suggests Boxcar Press plate Boxcar plate thickness Plate material Impression
0.8mm 94FL .94mm/.037” plastic backed shallower
1.52mm KF152 1.50mm/.060 plastic backed deep
0.9mm or greater 94SB .94mm/.037” metal backed shallower
0.9mm or greater 145HSB 1.40mm/.057″ metal backed medium
1.52mm 152SB 1.50mm/.060″ metal backed deep

Boxcar Press offers two options to metal clay artists. We can sell you unexposed polymer plates for do-it-yourself artists to create their own negatives and process themselves. Check out our new Plates by the Pound service for our plastic backed plates under our Supplies. Or we can take your digital files or images and professionally create plates for you, quickly and economically.

In either case, you will want to store your exposed plates in a zipper bag out of sunlight. You may also want to consider using a silicon spray to protect the plate from the moisture in the clay. You will want to clean the plate with vegetable oil.  Exposure to too much light and moisture will cause your plates to deteriorate.

Remember, we’re a letterpress shop, and letterpress is our expertise. We can’t answer specific questions about how our plates work with your process, but we can offer information on the polymer plate material, thickness, exposure times, and processing.

For additional information, you may also want to check out:

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How do I use a Stouffer Gauge to help process my plates?

Instructions for using the Stouffer Gauge to accurately figure out the exposure time for your photopolymer plates: The Stouffer gauge is a reusable piece of continuous-tone film that you should use to test photopolymer plate exposures. Place the Stouffer Gauge in contact with a 1” x 6” strip of plate material (after you peel off the plate’s protective plastic cover). Then expose the plate.

You’ll have to guess the first exposure time because that varies depending on the equipment that you use. Start with the exposure time listed on your plate’s tech data sheet. For exposure times, please keep in mind that these times are for commercial photopolymer platemaking equipment. Any alternative photopolymer platemaking devices may have very different times and you’ll have to experiment more to find your ideal time.

Also check the plate’s tech data sheet for the Stouffer value you’re trying to hold during exposure. For example, the 94FL has a Stouffer value of 18. Make sure that the exposure used with the Stouffer Gauge hardens the plate for all the numbers up to and including #18. If you goal is #18, and #19 and #20 start to harden during your exposure time, then your exposure time is too long– decrease the exposure time. If your goal is #18, and #17 hardens but #18 washes out on the test plate, then increase the exposure time.

You most likely will have to expose several different test plates at several different exposure times to find the perfect exposure. Since the Stouffer gauge is small, you won’t waste much plate material in the process.

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Can I mount your plates on wood?

We don’t recommend it. If you are determined to use wood, however—know that, even after your lengthy set-up time that will be required of you, you’ll still see uneven printing if using a wood base. Wood simply isn’t a flat enough surface to print on.

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What’s the smallest type size you can hold in your platemaking?

This question is not as straightforward as it seems. We can hold a 3 pt. Times New Roman type face on 94 and 95 plate material but the real question is the next one about the thinnest line and dots the plates can hold. The font choice and characteristics of the font may limit the point size.

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What’s the thinnest line and smallest dot you can hold on a plate?

It depends on the plate (though no hair lines, please!). If your plate has a 94 or 95 in the product name, we recommend at least a 0.25 point thickness (or larger). If your plate has 145 or 152 in the product name, we recommend at least a .35 point/.007″ thickness (or larger). Watch out for typefaces with swirly curves that thin or have breaks or fonts with fine cross bars.

For dots, we recommend at least a 1 pt diameter if your plate has a 94 or 95 in the product name. Boost that to 1.25pt diameter for plates that are 145 or 152 in thickness. Each of those dots has to stand on it’s own on the plate and that thickness will provide the support at the base of the plate to hold the dot. Watch out for typefaces where the dots on the “I’s or periods are small, as seen in many sans serif fonts that are decorative, free form or look hand drawn.

Undersize lines and dots may appear on your plate as wavy or be missing completely so checking this is very important for a good file and usable plate.

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