What's the difference between dry printing and wet printing?

Apr 23, 2012, 9 AM

By Janet Klug

In the routine of mounting stamps in an album or seeking information in a catalog, stamp collectors unearth terminology that may seem puzzling. Two such terms, wet printing and dry printing, are the subject of this Refresher Course column, suggested by Linn's reader Bill Stahl.

Wet printing and dry printing are terms used primarily in intaglio printing, which is also known as engraving, line engraving or recess printing. That is the method of production that involves a softened metal plate onto which a human engraver or a machine has carved a design.

There are multiple steps involved that transforms the carved or engraved metal plate and converts it into a printing plate. The printing of classic stamps required a lot of hand work by skilled platemakers and printers.

The soft metal engraved block is called a die. In the classic printing process, a few proof images were often taken at this step to ascertain what the completed stamp would look like. Once the engraving was completed, the die was subjected to high heat to make it very hard.

Another batch of proofs might be made after hardening. If the proofs were satisfactory, the hardened die would be used to create a transfer roll.

A transfer roll is a cylinder of soft metal, usually steel, that is pressure rolled over the hardened die. The soft metal cylinder picks up the image from the die in relief. If you ran your finger over the image on the metal cylinder, you would feel bumps. If you ran your finger over the die, it would feel smooth with some of the areas being indented. All of the indented areas on the flat die became raised areas on the metal cylinder.

After it was hardened, the metal cylinder became the transfer roller. The transfer roller was rocked back and forth on a sheet of soft steel, also called a plate. This was repeated as many times as necessary to create the number of images to be printed from a single plate. Proofs might be made from the soft plate. The plate was hardened and additional proofs might be made after hardening. Once the plate passed inspection it was ready for printing.

To print from the plate, a layer of thick printing ink was applied to the plate affixed to the press.

A tool was used to spread the ink and insure that it collected in all of the engraved areas on the plate. Excess ink was wiped away and the plate was buffed to remove any remaining color.

A sheet of paper was fed into the press and the paper was pressed against the ink-loaded plate using significant force. The ink transferred to the paper. The paper was removed and the process was repeated for the next sheet of stamps.

That explains the steps used when sheets of stamps were printed by hand from flat plates, one sheet at a time in a hand-operated printing press. Today, many fewer intaglio printed stamps are made, but when they are, it is the work of machines that frequently do the engraving and platemaking, and even more machines printing on gargantuan rolls of paper at high speeds.

The high-speed production was enabled by a simple change in the printing process.

Paper was dampened prior to being run through the printing press up until the time of highly mechanized printing. There was good reason to do this. Dampening the paper softened it a bit and made the ink adhere better. But the added moisture made the stamp image not quite as crisp as it could have been.

Additionally, a bigger problem was that as the stamps dried they would shrink. Sometimes the shrinking was negligible, other times it was significant.

When mechanized printing came on to the scene, the dampened paper caused problems. It was softer, and large rolls of paper used in mechanized printing would tear if wet. Wet paper took longer to dry, made less crisp images and shrank. Printing directly on dry paper solved many problems associated with wet printing. The image detail was improved, there was no shrinking and the machinery used for printing was not compromised.

So that tells the how and why of wet versus dry printing, but stamp collectors also need to know the "what" part of the story: what's the difference between the two from a collecting standpoint?

You can both see and feel the difference between wet and dry printing. In wet printing, the ink on the stamp sinks into the moistened paper and even spreads slightly.

You can see that under magnification better than you can see it with the naked eye.

Shown at left in Figure 1 is Tonga's 2½-penny Queen Salote stamp (Scott 59), issued in 1934 on tortoise watermarked paper. It is a wet printing of the stamp.

Dry printing eliminates the slight fuzziness from the design. The images are sharper, and because the ink does not sink into dampened paper, the ink is raised to the point that you can actually feel the texture. At right in Figure 1 is the same denomination of the Tonga Queen Salote stamp (Scott 76), but this example is the dry printing, printed on crown and script CA watermarked paper.

The Scott Standard Postage Stamp Catalogue does not mention the wet and dry printings, but it is the fastest way to tell the difference between the two stamps without looking at the watermarks.

Look closely at the leaves on the bottom left side of the stamp at left in Figure 1. The detail in the leaves is missing because the ink bled just a little bit, enough to fill in the spaces between the fine lines. Now look at the same area on the stamp at right. Can you see the difference?

Other points for comparison are the shaded areas on Queen Salote's face and the palm fronds in the upper right corner. It is almost hard to believe, but the plates that printed these stamps were created from the same dies.

The Scott Specialized Catalogue of United States Stamps and Covers contains several paragraphs about wet and dry printing at the beginning of the U.S. 1954-68 Liberty Issue listings, with a list of stamps in that series that were both wet and dry printed.

Figure 2 illustrates the wet-printed United States ½¢ Benjamin Franklin stamp at left (Scott 1030a) and the dry-printed stamp at right (1030).

The differences can be spotted best in the detail in Franklin's hair, the crosshatching in the jacket around the denomination and a slight orange cast to the paper in the wet printing.

These two stamps should be in your collection for no other reason than to serve as examples and help you find other wet and dry printed stamps you might have.