Thursday, July 10, 2008

Spark Institute Now in Session

Professor James Curtis Watne
Lead Press Operator, Spark Industries

Disclaimer: These are methods that I've found to work for Spark. I make no claims to complete knowledge and I'm sure there are lots of other ways out there that I don't know about. But since continuous learning is part of any worthwhile craft, I'm happy to relay what I've figured out.

Letterpress and Solid Areas of Ink

Solid areas typically present a challenge when printing on a platen press. This is because of two main factors: inking and impression.

In their original uses, platen presses were not expected to lay down huge amounts of ink and so typically have two or three form rollers. In addition, the rollers must pick up ink from a disk or drum, then pass down over the form and back up. (A cylinder press such as a Heidelberg K or S continually supplies ink to four form rollers from sizable distributor rollers.) As the ink supply is not continuous, at a certain point the roller has used one full revolution of ink and ghosting can occur.

Impression is probably the biggest issue in laying down a large solid. A platen press must make the entire impression at once, versus a cylinder press which "rolls" the paper across the form, with only a narrow band of contact at any one time. A given platen press will have a limit in the amount of force it can exert before something gives. As these machines are no longer made, we don't want to push them near that point! The Heidelberg windmill platen does have a shear collar which is designed to give way before something more expensive does, but a press such as a Chandler & Price will respond with a fracture in its cast iron. So one has to be realistic with what a machine can handle. If a client is set on having a full flood of ink across the back of their letterhead, it would probably be best to have that side offset printed. Printer and client will probably both be a lot happier!

Here's an order of approaches that I typically follow on the windmill for large solids:
1. heavy-ish inking with two rollers
2. add rider roller
3. two hits
4. skip feeding (this will be a future topic)

If I can tell at the start a job will need a certain approach I'll start with that. If coverage is insufficient then things get "escalated." A job may require the material to be split into two runs to achieve proper inking for a large solid along with a text area of the same color. Inking heavy enough for the solid to come out nicely can be way too much for the text area. Two hits with moderate inking can give the client's desired impression while being much crisper than one hit with heavy inking. Skip feeding allows two (or more) passes of the rollers, which works very well for eliminating ghosting and maximizing coverage. It requires quick, constant two-handed operation of the feed and impression with each sheet, and so is only really practical for short runs of special items. (This is one thing that is more easily accomplished on a hand-fed press such as a C&P where you only move the throwoff lever on and off, as feeding is at your manual control. You simply pause and let the press cycle once more, while having a leisurely interval to ready the next sheet.)

All of these approaches naturally require use of the ink fountain for consistency across a run. That's another topic for the future...

This example has a 5x7 full bleed solid on the back of 220 lb Lettra. The rider roller was employed, and two hits of ink were required.

This letterhead's large orange block was achieved with the rider roller and use of a thin rubber sheet in the packing. The French Durotone has a varied density throughout, and so does not lend itself to a smooth result easily. The rubber becomes in essence a variable packing to give more push behind the thinner areas. The back's full flood of orange was offset printed in advance, and the letterpress inking (from the same can) adjusted slightly to match. Our offset printer told us that even with their large press the backs required double hits of ink and as hard an impression as possible. Luckily the client expected and liked the slightly mottled look. The envelopes were printed flat on our Cylinder and converted.

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