Printing

Each character is cut in relief, reversed, on the end of a steel bar — soft steel for cutting, then hardened and tempered — see steel. Enclosed shapes — the inside of o, e, a — are struck in first with a counterpunch, then the outside is filed and gravered to shape.

Check each punch by smoking it in a candle flame and pressing it on paper, which gives a proof of the letter. Cut the whole character set to one design and one size.

Drive each punch into a copper blank to make a matrix — the mould for that letter. Then justify it: file the matrix so that the letter sits at exactly the same depth and on the same baseline as every other, and square to the mould.

This tedious filing is what makes type line up. An unjustified matrix casts letters that bob above or below the line on every page ever printed from them.

The hand mould — adjustable for width, fixed for height — is the actual invention: it casts thousands of identical, interchangeable letters.

Type metal is lead with antimony and tin — a classic foundry mix is roughly 60% lead, 25% antimony, 15% tin. Antimony expands slightly as it solidifies, so the casting fills the mould sharply; without it type is soft and blurred and wears out fast. Fix one type height for every piece of type in the shop and check every cast against a height gauge.

Lead poisons slowly and invisibly: stomach pain, anaemia, nerve damage, and permanent harm to children's developing brains. It enters by swallowing dust from hands far more than by breathing.

• No eating, drinking or smoking in the foundry or composing room.
• Wash hands and face before eating and before leaving.
• Melt at the lowest temperature that casts cleanly, with ventilation — fume rises sharply as metal gets hotter.
• Keep children and pregnant women out of the foundry.
• Wet-sweep, never dry-sweep, type dust.

Build it with your machine tool capability: a heavy screw, a flat platen, a moving bed that carries the locked-up type under the platen and out again. The platen and bed must be flat and parallel; check with the master flat.

Even pressure across the whole forme is what separates a legible page from a smudge. Put a padded tympan — layers of paper or felt — between platen and sheet to even out small differences. Test with a proof of a solid block of type: an evenly black impression edge to edge means even pressure.

Water-based writing ink beads off metal type. Printing ink is lampblack ground into a varnish of boiled linseed oil, ground on a stone slab with a muller until no grit can be felt between the fingers.

Boiling linseed oil to varnish is a fire hazard — it was historically done outdoors, away from buildings — and must never be left unattended.

An error in a printed medical dose or a chemical proportion is now reproduced hundreds of times. Proofreading is not a nicety.

For every technical page: compose, lock up, pull a proof. Then one person reads the manuscript aloud while another follows the proof, marking every difference. Every number — doses, quantities, temperatures, dimensions — is then checked a second time by a different person against the original source. Correct the type, pull a new proof, and check the corrections.

In order of return:

1. The library's most-needed manuals — medicine, water, agriculture.
2. School primers — see teach the next generation.
3. The settlement's laws — see published rule.
4. The standards — measures, thread pitches, the calendar — see one metre, one kilogram. A printed standard is what makes a standard hold across a region.
5. The local agricultural record.

Record the title, date, run size and where copies went for every job.