Printing Press

The printing press presses inked metal type onto damp paper with a wooden screw, so one page of text can be copied hundreds of times in a day. Gutenberg combined it with cast movable type and oil-based ink around 1440, and within fifty years printing had spread across Europe.

What it is

A printing press puts ink on paper by pressure. Letters cast in metal are set side by side to form a page, inked, covered with a damp sheet and squeezed under a flat plate. Lifted off, the sheet carries a mirror image of the type, which reads the right way round.

The machine itself was an old idea. Screw presses had squeezed grapes and olives since Roman times, and papermakers used them to press wet sheets. What was new was the combination of the press with reusable metal type that could be cast quickly and to exact sizes, an ink that stuck to metal, and cheap paper.

How it works

The two halves of the hand mould slide to fit the width of each letter, while the height of every sort stays the same.

The work starts with the type. A punchcutter files the shape of a letter, in reverse, on the end of a steel bar. The punch is struck into a small block of copper, leaving a hollow letter: the matrix. The matrix goes into the bottom of a hand mould, the caster pours in molten metal, and a moment later he opens the mould and drops out a sort, a small bar with the letter standing on its end.

Gutenberg’s mould could be adjusted for a narrow “i” or a wide “M” without changing the height of the type. That is what lets thousands of separate sorts stand together and print evenly. The metal, an alloy of lead, tin and antimony, melts at a low temperature, fills fine detail and wears slowly.

Ink balls were stuffed with wool or horsehair and dabbed onto the type.

The compositor picks sorts from a case, sets them line by line in a composing stick and builds up the pages. The pages are then locked tightly in an iron frame, the chase, with wedges. The result is the forme, which lies on a flat stone bed in the carriage of the press.

A pressman dabs the type with two ink balls loaded with ink made from soot and linseed oil. His partner lays a damp sheet on the tympan, a hinged frame covered with parchment, and folds the frisket over it to keep the margins clean. Tympan and frisket fold down onto the forme. Turning the rounce winds the carriage in under the platen. A pull on the bar turns the screw a fraction of a turn, the platen presses down, and the sheet is printed.

How to build it

A working press needs a carpenter, a smith and someone who can cut letters.

Build the frame. Join two heavy upright cheeks of oak with a head at the top and a cross piece lower down, and brace the whole to the floor and ceiling. If the frame flexes, the impression blurs.

The hose slides through the till without turning, so the platen hung from it on cords comes straight down.

Make the screw and platen. A wooden screw of hard, close-grained wood such as box or pear, cut with a coarse thread, runs in a nut set in the head. Below the nut the screw turns inside a square wooden sleeve, the hose, which slides through a guide board, the till, and cannot rotate. The flat platen hangs from the hose on cords, so it moves straight down without turning.

Fit the carriage. A smooth stone set in a wooden box slides on rails under the platen. A rounce, a spindle with a handle and leather straps, pulls it in and out.

Cast type. This is skilled foundry work. Cut steel punches, strike them into copper and cast in a two-part mould, with the precautions below. Without a proper foundry, letters carved in hardwood end grain will print, though slowly and less evenly.

Make ink. Grind lampblack into linseed-oil varnish, oil already thickened by heating, until it is as thick as honey. Buy the varnish ready-made or have it made by someone experienced, because heating oil is a fire hazard.

Dampen the paper. Slightly damp paper takes ink much better. Stack it between wet sheets overnight.

Safety. Cast type only in a workshop set up for molten lead, with a temperature-controlled melting pot, fume extraction, a face shield, a leather apron and gloves. Molten metal splashes violently if it touches water or a damp tool, so preheat ladles and moulds. Lead is poisonous: never eat while working, keep dross and dust in closed containers and wash your hands afterwards. Rags soaked in linseed oil can catch fire by themselves as they dry, so spread them flat outdoors or keep them in a closed metal tin of water. Keep clear of the swing of the bar.

History and evolution

Movable type was first made in China. In the 1040s Bi Sheng printed with baked clay characters, a method recorded by Shen Kuo. Korean printers later cast type in bronze, and the oldest surviving book printed from metal type, the Jikji, dates from 1377. Printing Chinese characters, in China as in Korea, needs thousands of different sorts, which kept the method expensive.

Johannes Gutenberg, a Mainz craftsman trained in metalwork, worked on printing in Strasbourg from about 1437 to 1444. Witnesses in a lawsuit of 1439 speak of a press, lead and forms used in a secret venture, usually taken to be early printing. Back in Mainz, with money from Johann Fust, he printed the 42-line Bible between about 1452 and 1455. About 180 copies were made, most on paper and the rest on vellum; 48 or 49 survive.

The trade spread fast. By 1480 printers were at work in about 110 places, and by 1500 in about 270 towns, which had turned out over twenty million copies.

Around 1800 the Stanhope press, built entirely of iron, doubled the output. In 1814 Friedrich Koenig’s steam-driven cylinder press printed The Times at 1,100 sheets an hour.