Matrix Striking
Part of Printing
How to create the copper matrices used for casting movable type by striking steel punches into soft metal blanks.
Why This Matters
Every piece of movable type begins as a matrix — a small block of copper bearing the reverse impression of one letter or character. When molten type metal is poured into this matrix inside a hand mold, a single piece of type is cast. To rebuild printing from first principles, the ability to create matrices is foundational: without matrices, no new type can be cast, and printing is limited to whatever surviving type can be found and maintained.
Matrix striking is the bridge between the engraver’s art (cutting punches) and the typecaster’s art. The punch carries the letter in positive relief; striking it into copper creates the negative impression in the matrix; casting into the matrix produces the positive type character. This chain of operations, developed in Europe in the 1440s and refined over centuries, remains valid and achievable with basic metalworking tools.
In a rebuilding scenario, a skilled punch cutter and matrix striker can supply a print shop with new fonts of type indefinitely, replacing worn or damaged characters and expanding the shop’s typographic range as needs grow.
Materials for Matrices
Copper
Copper is the standard matrix metal because it is soft enough to receive a sharp impression from a hardened steel punch, yet hard enough to withstand thousands of castings without deforming. Pure copper works, but many historical matrices were made from a slightly harder copper alloy with a small percentage of tin.
Sourcing copper: Electrical wire, plumbing fittings, copper sheet, and old coins are all usable. Wire and thin sheet must be laminated or built up to the required thickness (typically 5–8mm for a matrix blank). Casting copper from scrap into small ingots is practical with a clay crucible and a charcoal fire.
Annealing: Before striking, copper must be fully annealed (softened). Heat the copper blank to a dull red heat and quench immediately in water. Unlike steel, copper is softened (not hardened) by quenching. Annealing relieves internal stress and ensures the copper will receive the punch impression cleanly without cracking.
Alternative Materials
Brass: Harder than copper and requires more force to strike, but produces matrices that last longer in casting. Requires heavier tools.
Lead alloys: Soft lead alloys can receive impressions easily but wear quickly in casting — unsuitable for long-term use. Acceptable for experimental or short-run type.
Hard wax or compressed graphite: Can receive impressions for testing punch quality, but not suitable as casting matrices.
Preparing the Matrix Blank
The matrix blank must be flat, clean, and of consistent thickness. Any variation in thickness causes type cast from different matrices to have different body heights, making the type impossible to set consistently.
Preparing the Surface
- Cut a blank slightly larger than needed (about 20% larger in all dimensions than the final matrix size).
- File all surfaces flat on a reference surface (a flat stone, glass, or machined iron plate) using a smooth file. Check flatness frequently with a straightedge.
- Polish the striking face to a smooth finish. The finer the surface finish, the cleaner the impression will be. Use progressively finer abrasive stones or sandpaper grades, finishing with the finest available.
- The striking face must be absolutely flat and free from scratches — any surface texture will appear in the cast type.
Sizing the Blank
Matrix blanks are typically rectangular, slightly wider and taller than the character to be struck. Standard dimensions for a blank for lowercase text type might be 8mm wide × 10mm tall × 6mm thick. Larger characters need larger blanks.
Mark the approximate center of the striking face where the punch will land. The letter impression should be centered horizontally and placed slightly above center vertically (because type bodies are taller than the letter itself, with space above and below for ascenders and descenders).
The Striking Process
Setup
Secure the matrix blank in a vise or on a hardened backing plate. The blank must not be able to shift or rock during striking — any movement produces a misregistered or smeared impression.
Place the vise and backing plate on a heavy, solid surface — a heavy workbench bolted to the floor, or a stone block. The impact energy must go into the impression, not into vibrating the workbench.
Test Strike
Before committing a finished punch to a good copper blank:
- Test strike into a piece of soft lead to verify the punch produces a clean, sharp impression.
- Verify the impression is centered and upright.
- Inspect the lead impression with a magnifier. Any defects in the punch — incomplete engraving, burrs, tool marks — will be visible in the lead.
- Correct the punch before proceeding to copper.
Striking into Copper
- Anneal the copper blank and allow it to cool to room temperature.
- Place the punch point-down on the polished striking face, centered as planned.
- Hold the punch perpendicular to the blank surface — a tilted punch creates a distorted impression.
- Strike the punch with a heavy hammer (500g to 1kg) in a single controlled blow. The goal is to drive the punch to the correct depth in one or two strikes rather than many light taps.
- Remove the punch carefully (a gentle side tap from a small hammer loosens it if it sticks).
- Inspect the impression.
Depth of Strike
The punch must penetrate to the correct depth — deep enough that the full letter relief is captured, shallow enough that the copper around the impression is not cracked or distorted.
For a text-size letter, a depth of 1.5–2.5mm is typical. The impression should show a complete, sharp rendition of every fine stroke in the letter. If the bottom of deep cuts (like the center of ‘e’ or ‘o’) appears flat or blunt, the punch was not driven deep enough. Strike again after re-annealing.
If the copper cracks or lifts around the impression, the strike was too deep or the copper was too hard. Anneal and use a fresh blank if the crack is in the impression area.
Multiple Strikes
If the first strike does not capture the full impression depth, the blank can be re-annealed and struck again — but only once or twice. Repeated striking work-hardens the copper around the impression, making it increasingly difficult to drive the punch deeper without distortion.
Between strikes, anneal the blank again (even after a second strike). Do not attempt to deepen a partially struck impression in un-annealed copper.
Finishing the Matrix
After striking, the matrix requires adjustment and finishing before it is ready for casting.
Justification
The struck impression must be positioned precisely relative to the matrix body. “Justifying” a matrix means filing and fitting it so that type cast from it will sit at the correct height, width, and alignment relative to all other type in the font.
Use a small flat file to adjust the matrix body dimensions. Check against a set of already-justified matrices or against a calibrated reference block. For a font being established from scratch, establish one reference character (typically the capital ‘M’ or the lowercase ‘n’) and justify all other matrices relative to it.
Cleaning the Impression
After striking, fine copper burrs may be displaced into the impression. Use a sharp graver or fine steel wire to clean these out without touching the struck surfaces of the letter. Blown with a breath of air, then inspected under magnification.
Fitting the Matrix to the Mold
Test the matrix in the hand mold before committing to a casting run. The matrix must seat flat in the mold, with the impression correctly positioned at the casting opening. Cast a single test piece and inspect it: the letter should stand centered on the type body, at the correct height, with clean form.
Adjust matrix fitting and re-test until the cast type is correct. Only then move to full production casting.
Tools Required
| Tool | Purpose | Notes |
|---|---|---|
| Hardened steel punches | The actual letter forms | See Punch Cutting article |
| Heavy hammer (500g–1kg) | Driving the punch | Steel face, no bounce |
| Copper blanks | The matrix material | Annealed before use |
| Vise or backing plate | Holding the blank | Must be rigid |
| Flat reference surface | Truing blank faces | Granite, machined iron, or thick glass |
| Smooth files | Finishing blank faces and justification | Mill file + needle files |
| Fine abrasive stones | Polishing striking face | Oilstone, Arkansas stone |
| Magnifier | Inspecting impressions | 5–10× loupe |
| Small graver | Cleaning impression | Sharp steel graver or dental pick |
Matrix striking is a skill that rewards patience and precision. A well-struck, properly justified matrix produces useful type for decades of casting — an investment of several hours that pays dividends with every book printed thereafter.