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by Jerry Oltion

The Science of Printing


I used to be a devil. That's a technical term used in the printing industry for a printer's assistant. We're the guys who haul paper around, mix ink, run folding machines, cut apart multiple-image print jobs, collate, staple, etc. Mark Twain was a printer's devil, so I'm in good company.

Printing has come a long way since Gutenberg, and in fact Gutenberg was just a major player in a much longer chain of innovation dating back to triangular wedges and clay tablets. It's an interesting history, and the technological advances are even more so. Let's have a look at the science of printing.


The Early Tech


Not surprisingly, the history of printing starts with the history of writing, because for millennia the only way to copy something was to re-write it. Advances in printing were basically advances in writing instruments, all with the goal of making the writing process smoother, easier, and faster. The pinnacle of writing instruments is often considered to be the Montblanc fountain pen, although I might offer the simple Bic ballpoint as a pretty close second due to its sheer utility.

Handwriting is a slow, painstaking, and error-prone operation. That meant copying a book was expensive and time consuming. Most books were duplicated by monks, who were about the only people with the patience to do it. So books—and pretty much anything written—were for the rich.


Wood on Wood (Xylography)


The first instance of what we would call printing was probably the woodblock, developed in China around AD 200. Oddly enough, its first use was in printing images on fabric, because paper wasn't yet in common use. The image to be printed was carved into a block of fine-grained wood; or rather, the image was left untouched and everything that wasn't to be printed was removed, leaving the image standing up above the background. Ink was then spread over the raised image, and the inked wood block was pressed into the fabric. When paper became common, woodblock printing was adapted to text and documents. Each character had to be carved by hand—backward!—and woe to the engraver who made a mistake after 9/10 of the block had been carved, but once the block was complete it could be used to make thousands of copies, which was still a vast improvement over hand-copying that many documents.




Then around AD 1040, a Chinese inventer named Bi Sheng got the bright idea of making woodcuts of individual letters (actually using clay instead of wood), and assembling them in order to make sentences, paragraphs, and whole pages. After the requisite number of copies of that page had been printed, the master page could be disassembled and the letters used again to make up another page.

Not surprisingly, the idea didn't catch on. For one thing, with over 40,000 characters the Chinese language doesn't lend itself to moveable type. For another, once a woodblock was created it could be stored, whole, and reused on a moment's notice, producing an exact copy of the first printing. With moveable type, each time the printer wanted to reprint a document, they had to recreate the entire page from scratch. That recreation inevitably contained errors that had to be corrected, which made the whole setup nearly as difficult as creating a more permanent woodblock.

Moveable type didn't really take off until Johannes Gutenberg got hold of the idea around 1450. His Gutenberg Bible, published in 1455, was the turning point. It made Bibles cheap enough for common people to buy, which in turn led to more people learning to read, which created a demand for books and magazines that has continued unabated to this day.


The Press


Gutenberg made his type out of an alloy of lead, tin, antimony, copper, and bismuth, which has remained the mix for moveable type even now. The greatest innovations between the 1400s and the 1950s were in the design of the gadget that squeezed the paper into the inked page of type. Not surprisingly, that gadget is called a "press."

Early presses were just frameworks with a big flat plate pushed downward by weights or by a big screw. They were time-consuming: The operator had to ink the type, lay the paper (carefully!) on the type, lower the platen onto the paper, press it hard, raise it back up again, remove the paper and set it aside to dry, then do the same thing over again. At peak efficiency, a skilled team of operators could produce a page every fifteen seconds: 240 pages per hour. That was a huge advance over hand-copying, but it was just the beginning.

The first major advances in press design came with automating the various processes. Rather than have the devil smear ink over the type with two dogskin pads (because dog skin doesn't have pores), an ink-covered roller could be swept across the type block while the platen was being pulled back for unloading. The paper itself could be swept in and out of position on "windmill" arms. The entire works could be driven by a treadmill, and later, steam engines and electric motors. (When I graduated from devil to pressman, one of my great joys was to run the Heidelberg Windmill press, an amazing piece of technology still in everyday use in 1980.)

Improvements in press design were only half the equation, though. Picking individual letters out of a case1 and assembling them into a "chase" was time-consuming work, and prone to error. The letters had to be backward so they would print correctly, so the compositor had to learn how to read backward. Even so, it was easy to get a "p" or a "q" rotated wrong, which accounts for the phrase, "Mind your P's and Q's."




Many attempts at automating the setting of type were made. Mark Twain lost his fortune on the Paige Compositor in the 1870s, and there were many other notable failures. It wasn't until the 1880s with the introduction of the Mergenthaler Linotype machine that typesetting was truly automated.

The Linotype machine had a 90-character keyboard, and each time a key was pressed, the machine dropped a little block of type (a matrix, or "mat") carrying a single letter at its tip into place in the assembler, then when a line was complete, that "line of type" would be flooded with molten lead, which would form the text for one line in the document. The lead "slugs" would all be collected in order in a tray called a "galley," then packed into a frame called a "chase" (and tightened in place with a "quoin," using a "quoin key" to snug it up). "Galley proofs" were made by inking the type while it was still in the galley and pressing sheets of paper against the inked type. Proofreaders would check for mistakes, and any that were found would mean re-typing the whole slug, and often the entire remainder of the paragraph if the correction changed the ending of the line it was on.


Warp Speed


The Linotype machine dramatically sped up the composition stage, and motorizing dramatically sped up the presses, but there was a limit to how many cycles per minute a press could make. All those back-and-forth motions could only go so fast before the machines shook themselves apart. We needed a better system, and it turned out that had already been invented in the early 1800s: Rotary printing.

In a rotary press, the flat block of type is replaced by a "stereotype" or "cliché,"2 in which a mold is cast over the type, then another positive image is cast into the mold and curved around a drum on the press. That drum rests against another drum and the paper is fed between the two drums, pressing the type into the paper as it rolls past. Ink rollers above the print drum keep it constantly inked, and automatic feeders keep the paper flowing.

Paper is made in big rolls called "webs," so it was only natural to skip cutting it into sheets until after it was printed. Modern "web presses" take entire rolls of paper, sometimes miles long, and print on them at speeds up to 20 miles per hour.




"Hot type," as the Linotype system is called, still had its drawbacks. The typesetting machine needed a reservoir of molten lead, chases full of finished pages were heavy and easily spilled, storing clichés was space-intensive, re-melting the ink-covered type was smelly, and so on. Printers kept looking for a better system, and it wasn't long in coming. About the time the Linotype was invented, in fact, the first "offset" presses were being developed. The technology didn't really take off until the 1950s, but once it did, it rapidly took over.

Offset printing uses a flat plate on which the type has been photographically etched. The plate is essentially an aluminum-backed photograph of the printed page, in which the parts that are supposed to carry ink are made of a water-repelling material, and the non-inked areas are bare aluminum. (Certain plastics can also be be used for the substrate.) The press has ink rollers just like before, but it also has a water roller that gets the plate wet. The ink is oil based, and we all know that oil and water don't mix, so the bare aluminum parts of the plate get wet and repel the ink when they pass the ink roller, but the parts of the plate that repel the water don't repel the ink, so they turn dark.

You'd think the next step would be to press the inked plate against the paper, and that's exactly what the first offset presses did...until a press operator in 1901 noticed that when he missed loading a sheet of paper and the inked plate transferred its image to the "blanket" (the rubber cylinder that pressed the paper into the plate), the resulting image on the back of the next sheet was crisper and more contrasty than the front-side image. So presses were redesigned to make the plate print onto the rubber blanket, which in turn transferred the image to the paper.


Current Day


Nowadays typesetting is done on a computer, and the plates are etched by a laser much like in a home laser printer. Books and magazines like Fantasy & Science Fiction are printed in "signatures" of 8 or 16 pages each that are cut off the web at the output end of the press, folded, collated with other signatures, bound, and trimmed without a hand touching them.

Other books use an even newer technology: Print on Demand. A print-on-demand press is basically a big laser printer, which is essentially a photocopy machine with a computer-generated original rather than a printed original, and it produces an entire book at a time, one page after another. If you want two copies, it prints one, then prints another.

Just like medieval monks did a millennium ago.



1  Capital letters were kept in the upper part of the case, hence "upper-case" letters.

2  And now you know where those terms come from.


Jerry Oltion has been a science nut since he was old enough to spell "curious." He has written science fiction almost as long, and has done astronomy somewhat less. He writes a regular column on amateur telescope making for Sky & Telescope magazine, and spends many, many nights a year out under the stars.

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