Type Casting
Part of Printing
How to cast movable type from molten metal using a hand mold and copper matrices.
Why This Matters
Movable type is the technological foundation of printing. Each piece of type — a single letter cast in metal alloy — can be set into words, inked, printed thousands of times, cleaned, and reset in a different arrangement to print something entirely new. This reusability is what makes printing economically viable: the investment in type creation is amortized across millions of impressions.
Type casting is the process of producing these small metal letters by pouring molten alloy into a hand mold fitted with a copper matrix. The process is straightforward enough to be learned in a few weeks of practice. A proficient caster can produce 300–500 pieces of type per hour. A modest print shop requires perhaps 5,000–10,000 pieces of type total — a week or two of casting to establish, then occasional casting to replace worn or lost pieces.
In a rebuilding context, the ability to cast your own type means independence from external supply chains. With matrices, a mold, alloy, and a fire, a community can maintain and expand its typographic resources indefinitely.
The Type Metal Alloy
Type is cast from a specific alloy — not from pure metals — because the alloy has properties that pure metals lack.
Why Alloy?
Pure lead is too soft — it deforms under printing pressure and wears quickly. Pure tin is expensive. Antimony, when alloyed with lead, does something remarkable: the alloy expands slightly as it solidifies (rather than shrinking like most metals). This expansion forces the molten metal into every detail of the matrix cavity, producing sharp, complete letter forms.
Traditional Type Metal Composition
| Metal | Percentage | Function |
|---|---|---|
| Lead | 75–80% | Base metal, melting point control |
| Antimony | 15–20% | Hardness, expansion on solidifying |
| Tin | 5–10% | Fluidity, strength, surface quality |
This alloy melts at approximately 240–260°C — low enough to melt over a modest charcoal or wood fire — and solidifies quickly when poured into the mold, allowing rapid casting.
Sourcing Metals
Lead: Very widely available from plumbing pipes, weights, cable sheathing, old batteries (but battery lead contains calcium or antimony already — composition varies). Sheet lead roofing is pure lead.
Antimony: Less common. Natural stibnite (antimony sulfide, a gray metallic mineral) can be smelted to extract antimony. Salvaged from old hardware (some bearings, type metal scraps, certain alloys). Worth significant effort to obtain — the printing quality difference between type cast with and without antimony is dramatic.
Tin: Available from tin cans (though modern “tin” cans are mostly steel with a thin tin coating — melt many cans to recover small amounts of tin), solder, pewter. Pewter is an excellent tin source.
Alternative alloys: If antimony is unavailable, a lead-tin alloy (70% lead, 30% tin) produces acceptable type — softer and less dimensionally stable than the traditional formula, but usable for moderate print runs.
The Hand Mold
The hand mold is the device that forms the body (shank) of the type while the matrix forms the face (the letter surface).
Mold Design
The hand mold consists of two L-shaped iron or brass halves that fit together to form a rectangular cavity. The cavity dimensions determine the type body — the width and depth of the metal shank.
Body size: The body depth (the dimension that determines type size) is fixed for a given mold. Text sizes typically range from 6 to 24 points (approximately 2–8mm body depth). A mold is dedicated to one body size.
Set width: The body width varies for each character (a capital ‘M’ is wider than an ‘i’). The hand mold adjusts its width by slightly opening or closing the two halves. The matrix, seated at the bottom of the mold, controls the face width. The mold must be adjusted for each different character being cast.
The matrix seat: At the bottom of the mold cavity, a recessed slot receives the copper matrix face-up. The matrix must seat flat and firm, correctly positioned so the letter face aligns precisely in the finished type.
Mold Construction
Building a hand mold requires accurate metalworking. The two halves must mate precisely, with no gaps, and must open and close smoothly without play. Historical molds were made from iron, sometimes with brass for the inner surfaces.
For improvised construction, the key requirement is flat, accurately mated mating faces and a secure but adjustable closure mechanism. A simple wooden mold lined with thin sheet iron can function for exploratory casting, though durability and precision are lower than an all-metal mold.
Casting Process
Setting Up
- Build a fire or establish a heat source capable of reaching 300°C reliably. A charcoal fire in a small forge or a clay fire pot is adequate.
- Melt the type metal alloy in a small iron ladle or pot. Maintain the melt at working temperature (about 40–60°C above the melting point). Too cool: the metal solidifies before filling the mold. Too hot: it damages the matrix and produces rough castings.
- Skim any oxide dross from the surface of the melt before each pour.
- Seat the first matrix in the mold. Verify it is flat and properly positioned.
- Close and secure the mold halves.
The Casting Motion
Casting is done with one continuous smooth motion:
- Hold the mold in one hand (typically the left), with the pour opening facing up.
- With a small ladle or spoon (the casting ladle), scoop a small amount of molten metal.
- Pour the metal into the mold with a smooth, quick motion. Simultaneously jerk the mold upward slightly (the “throw”) — this motion drives the metal into the matrix and prevents a cold shut (solidified metal in the pour channel that didn’t fully fill the letter form).
- Hold for 2–3 seconds while the type solidifies.
- Open the mold and eject the type by pressing the ejector spring or tapping the mold.
- The type falls out as a complete casting with a sprue (the excess metal from the pour channel) attached.
The entire motion — ladle, pour, throw, hold, eject — takes 4–6 seconds. With practice, it becomes completely automatic.
Breaking Off the Sprue
Each cast type has a small fin or tail of metal (the sprue) attached where the molten metal entered the mold. This must be broken off cleanly. A sharp tap against a metal edge breaks the sprue; a quick swipe with a file smooths the break point.
The sprue metal falls into a recovery pan and is re-melted for future casting.
Finishing the Type
After breaking off the sprue, each piece of type needs two finishing operations:
Breaking: A small nick on the side of the type body where the mold halves met is rubbed smooth on a flat abrasive stone. This removes any flash or sharp edge that would prevent the type from seating flat in the composing stick.
Height dressing: The foot of the type (the bottom, which rests on the press bed) may have slight irregularities. For type that will be used in a precisely set form, dress all pieces to the same height by rubbing the foot gently on a flat abrasive surface. All type in a font must be the same height (“type high” — approximately 23.3mm in traditional European printing, though a community can establish its own standard as long as it is consistent).
Quality Control
Inspect each piece of type as it is ejected:
- Face complete: All letter details present, no flat spots where metal failed to fill the matrix.
- No bubbles: Pinholes or bubbles indicate the metal was too hot or the pour too slow.
- Square body: The type body should be rectangular, not twisted or warped.
- Face correctly positioned: The face should be centered (or correctly offset for the typeface design) on the body.
Defective type goes directly back into the melt. Do not allow poor type to accumulate in the cases — it will cause print quality problems that are difficult to diagnose.
Establishing Type Font Quantities
A working type font needs multiple copies of frequently used letters. English letter frequency guides minimum quantities:
- High-need (cast 12+ of each): e, t, a, o, i, n, s, h, r
- Medium-need (8–12 each): d, l, c, u, m, w, f, g, y, p, b
- Lower-need (4–8 each): v, k, j, x, q, z
- Capitals: 4–8 of each
- Digits: 6–10 of each
- Common punctuation (., , ; : ): 10–20 of each
For a 100-character-per-line composition at typical speeds, a working stock of approximately 3,000–5,000 pieces per typeface/size combination is a practical minimum.