Friday, February 22, 2008

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!


Grizzly Mountain Arts said...

Very interesting blog!

~Stella said...

Oh, my! Great tutorials and LOVELY blog!


laura said...

your blog is so inspirational and educational to someone like me who dreams of making those beautiful cards. please keep it up!

Block Printing said...

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Holly said...

I couldn't find any clear explanation online for creating custom letterpress plates until I came across your informative, super-helpful post! Thank you so much! :)