Letterpress Step 3: Making a photopolymer plate out of your illustration

So here we are at the third installment of the process of getting from illustration to letterpress product. In the first installment we made a simple two-color illustration on the computer using a favorite photograph. In the second step of the process we prepped that file for printing. At the end of the second step, with the consideration of the unique requirements your personal printer or plate-maker might have, you were ready to send your file off to have a plate made for you. In the case that you are sending your files off to be made into a plate, this information will be purely for your curiosity about what's going on behind closed doors at plate-makers' shops. (If you'd like more information about the process vis-a-vis working with professional plate-makers, check out Boxcar Press.

If you are interested in using a photopolymer plate making lab which may be available in some printmaking departments or studios, this information will be valuable to you. While I describe the process that I use to make the plates, I'll inject a few interesting resources I've found on the web that document inexpensive ways to set up a plate-making operation in your own home, although I have no experience doing it in that fashion.


Step 1: At the end of the last installment we had separated the two colors but had left them in their appropriate Pantone colors. In this step we need to convert each colored portion into plain black. Remember that grays or halftones do not work well in this process, so make sure everything is either black or white.



Step 2: Resize the images to be the same size as they will appear on your final letterpress product. If you'd like to use the same image in multiple sizes, you'll need to make multiple printouts and multiple plates. I've combined both images onto one 8.5"x11" page and printed a single copy. If you are interested in drawing something by hand with traditional pen & ink you can skip to this step in the process and use that illustration to make a negative directly.


Step 3: A negative needs to be made from your printout. Using a film negative service will produce a superior negative, but if you're doing it low budget or doing it at home, a transparency from a copy machine will work just fine. Load the transparencies into the copy machine and select "Negative/Positive" (may differ from machine to machine) and create a negative of your printout. Since transparencies are not quite as opaque as film negatives it's a good idea to make two copies, line them up exactly, and tape them together (being careful not to cover any of your art).



Step 4: This step needs to be done in a darkroom environment because the plates are light sensitive. If you decide to set up shop at home, you can purchase virgin plates from Boxcar Press in various sizes & widths. If necessary, cut a plate to fit the size of your negative – it can be smaller but make sure all your art is on top of the plate. All the photopolymer plates I've worked with have a side with a protective cover on it. Peel that off when you're ready and flip your negative face down on top of the freshly peeled side. Looking at it, your art should now be backwards.


Step 5: In order to "burn" your image onto the plate, you need to expose the plate to light. Thankfully I have access to a lab with a big expensive machine that has a vacuum action to pull the negative tightly against the plate and expose the plate to the light needed. With any machine or even in your own home if you don't have resources with recommended exposure times, you may have to do a little experimentation to get it just right. Exposure times can also differ depending on the weight of your lines or the intricacy of your design, I've found.

There's a DIY tutorial for making photopolymer plates in your own home by Maggie Bergman that I've found at Silver Clay Art. She details some of the above steps as well, but most importantly talks about how to clamp a negative to the plate using clips, expose using fluorescent or halogen lights, and how to make test strips. All very important things if you're interested in doing this at home.



Step 6: (This step should be done in a darkroom environment.) If you have a plate-washing machine you can use that (I do about 6 minutes this way), but if not use a soft brush and water to rub away the part of the plate that was not touched by light coming through your negative (aka the white space in your original). The plate will feel slimy (and be kind of smelly) during this process. You want to continue lightly scrubbing until the details of your design start to feel sharp-edged under your fingers. If there are little bumps in the middle of white space areas or the plate still feels really slimy, you need to scrub a little more. Don't scrub too vigorously or too long – you may end up with no design at all! Maggie Bergman recommends 2-3 minutes of scrubbing to get it cleaned out when doing it by hand. When you're all done you'll see what will be the colored part of your design raised in the plastic.


Step 7: (This step does not need to be done in the dark.) Before you use your plate it's important to firm it up. I use a little plate oven that's at about 80 degrees Celsius for 5-6 minutes, but Maggie Bergman recommends using a blow dryer or fan heater at home. I've seen someone somewhere talking about nail polish hardening machines, too. :-) You don't need to completely dry out the plate – it should still be flexible when you're done and not overheated. Sometimes over drying can warp thin lines or even make the plate start to split into layers.



Step 8: This step is more of a precaution to make sure that all parts of the plate have been exposed by giving it a little more light.

Letterpress Step 2: Prepping Files for Photopolymer Plates

In the first post of this series we turned a regular photo into a two-color computer illustration. For the next step, we need to get this image ready for printmaking. For those of you familiar with prepping files for offset printing some parts of this process will come naturally and others will be counterintuitive.

Most of today's letterpress printing of images/illustrations is done using photopolymer plates. Photopolymer plates are light sensitive plates onto which light "burns" a negative of your desired image. The area that light touches remains raised and the rest is washed away, leaving you with a surface akin to linoleum or wood carvings (in the sense that the raised part represents a flipped image). I'll talk about the process of making plates a little in my next post.

I think it's safe to say that most letterpress printers do not have access to plate-making equipment, but rather order their plates. One of the most notable photopolymer plate-makers is Boxcar Press here in New York state. Other businesses who offer letterpress parts & supplies sometimes process plates as well, like NA Graphics in Colorado.

Let's get our illustrations ready for new plates!





Step 1: When deciding on an illustration to use for letterpress, you need to make sure that it fits the limitations that letterpress presents. If you are designing your first project for letterpress, take a look at Boxcar Press' "Seven Easy Steps to Photopolymer Perfection" for some tips. I've outlined a few of their more general tips above.

The major reason that letterpress printers ask you to use Pantone colors is because letterpress printing doesn't work in the way that offset printing does – a 4-color [layered] process using CMYK cannot be applied the same way. Pantone inks used in offset printing can also be used for letterpress printing, so custom printers will have them on hand. They can often find your ink color on their shelves or get it mixed for you. An unspecified color would have to be matched to a Pantone color or in some cases, hand-mixed. Each different color, even different screens of Pantone colors that you would consider a single color in offset printing, are a unique pass through the letterpress. This leads us to the next step...




Step 2: Looking at my illustration of the holly, I have two distinct colors Pantone 1805 (the red) and Pantone 4625 (the brown). If I had originally had more colors than this, this could have been the time to simplify the illustration. An example of simplification could be changing Pantone screens into 100% color or white to eliminate the need for more colors. Each distinct color requires its own photopolmer plate & a unique pass through the letterpress, so the fewer colors the better.

Getting the files ready for making plates takes a little bit of pre-press work. In off-set printing many of the following decisions are made for you by the printer's pre-press department, but when you're making plates you need to decide how to treat your files. Registration (or the alignment of multiple colors) is tough in letterpress & takes a lot of time to get right. That's why you'll see many designs that avoid perfect registration by not having objects overlapping or intersecting. I designed this illustration early on and hadn't considered the difficulty of printing it.

The following are some pre-press methods for separating your colors....


Knockout: Knockout creates a white hole underneath the object on top. This way colors that appear to the eye to be overlapping are both being printed directly on the paper rather than one on top of the other, each showing its truest possible color.



Knockout Problems: The problem with knockout is that it doesn't give you any margin of error in registration. If registration is the slightest bit off then white space will show up between the two objects that are supposed to appear to be overlapping. This problem was inescapable for me with the Christmas cards since I chose this method of preparation. In the end, I really enjoyed the off-kilter effect, but that's not to say you will in your work.



Overprint: Overprinting can create some really cool effects in letterpress (which I look forward to exploring myself in the future), although it's not always fun if you don't mean for it to happen. Rather than creating a white space beneath the top object, overprinting does exactly what it sounds like it'd do: one pass of ink goes right over the other. Click on the picture above for more detail and you'll see the darkened areas that result on the berries because of the red ink combining with the brown ink.


Trapping: Trapping can sometimes combine the best of both worlds by creating a margin of error for the knockout method. By slightly increasing the size of the object on top, it is able to move slightly from perfect registration without exposing any white below. At the same time, you'll have a tiny bit of overprint effect on the edges where the colors overlap (overprinting is exaggerated above for visibility).


Step 3: For my image, I've decided this time to overprint the brown ends on the berry and use trapping to make sure branches & berries meet. Step 3 involves separating the two colors. What I do is draw an outlining box or create crop marks to remind myself later how the two images align (this can be very important when trying to get things lined up on the press). Sometimes it's even required by plate-makers or letterpress printers who'll be using your custom artwork for printing.

Once you have an outline around the whole image you can copy & paste so you have two identical images. I chose one image to represent the plate that will have the brown ink, so I convert all the red berries in that image to white. Then I did the opposite with the "red plate" image. Now I have two images that represent the two plates I'll need to "reassemble" for the final letterpress product.


Step 4: Aside from the color separations & initial considerations for your image, getting your files to your printer or plate-maker doesn't differ greatly from what you need to do for offset printing. Each printer may ask for different things, but I've put a few common requests above. If you're a letterpress printer looking to make plates for home, or if you're just curious about the process, check out Boxcar Press' tips on preparing your files (including an elaboration of some of the tips in Step 1) or their pricing & turnaround info here.

If anything needs clarification or correction, please let me know!