Deadwax Reference · Runout Groove
Every vinyl record carries a hidden fingerprint etched into the smooth ring near the label. Learn to read it and you can tell exactly which pressing, which cutting engineer, and sometimes which plant made the copy in your hands.
A matrix number is the alphanumeric code etched or stamped into the runout groove — the smooth, ungrooved ring of vinyl between the last track and the record label. Collectors usually call this area the dead wax. It's added during mastering and pressing, not printing, so it can't be faked or reprinted the way sleeve artwork can.
The catalog number on the sleeve tells you what release you're holding. The matrix number tells you exactly which cut, master, and pressing run produced that specific disc — two copies with identical covers and barcodes can carry completely different matrix codes, and therefore be worth very different amounts.
To read one: hold the record under a bright light at a low angle so the light rakes across the surface, and rotate it slowly — the etching is often faint and easy to miss under flat, direct light.
The cutting engineer etches the audio into a soft lacquer disc — this is where hand-etched matrix numbers and engineer signatures usually originate.
A metal positive is grown from the master. It's never used to press records directly — only to grow stampers — and is numbered so plants can track which mother made which batch.
A metal negative grown from the mother, fitted into the press. This is the part that actually strikes the grooves into your copy, and it wears out over a run.
Yields are rough industry rules of thumb, not fixed figures — they varied by plant, era, and how hard a stamper was pushed before replacement.
The main code, often matching or closely resembling the sleeve's catalog number, plus a take or cut suffix like -1 or -2.
Usually a plain number showing which mother the stamper for this copy was grown from.
Often a coded letter rather than a number — some UK plants spelled it using a company word (see below).
This 12/9/3 layout shows up often enough to be a useful starting point, but spacing varied wildly by label and plant — some crammed everything onto one line, others scattered marks anywhere around the ring. Treat it as a place to start looking, not a guarantee.
Format and library prefix plus a unique reference number for the release — mono 12" LPs on this label used the prefix XAX, stereo used YAX.
The take or cut number — this was the first lacquer cut for this release. A later recut might show -2 or higher.
A coded stamper letter. Some UK plants spelled these using a ten-letter company word standing in for the digits 1–10, so the letters themselves aren't arbitrary — they map back to a specific stamper number.
Every label and country had its own numbering habits — treat this as an illustration of the logic, not a template every record follows exactly.
Look at the smooth, ungrooved ring between the end of the final track and the label — on a 12" LP it's usually a band around 1–1.5cm wide.
Hold the record at a shallow angle under a strong point-source light so it skims the surface. Flat overhead light hides etchings completely.
Codes aren't always grouped together — rotate the full circumference, since different marks can sit at completely different points.
A 5–10x magnifying loupe helps with hand-etched codes, which are often finer and less regular than machine-stamped ones.
Include dashes, spacing, and capitalization. Small differences (a stray letter, an extra dash) are often the entire difference between two distinct pressings.
The A-side and B-side matrix codes are almost always slightly different — if they're identical, double-check you haven't copied the catalog number by mistake.
| Mark | Engineer | Known for |
|---|---|---|
| RL | Robert Ludwig | Masterdisk and Sterling Sound cuts, widely chased for sound quality — including the sought-after "hot mix" of certain 1970s rock LPs. |
| BG | Bernie Grundman | Long-running mastering engineer credited on a huge range of major-label US pressings. |
| PORKY / A Porky Prime Cut / Pecko Duck | George Peckham | UK cutting engineer who signed thousands of records, from The Beatles' Apple releases through UK punk and new wave. |
| HTM | Harry Moss | UK mastering engineer often cited alongside early-catalog-number UK pressings from the 1970s. |
| LH / TJ | Lee Hulko / Ted Jensen | Sterling Sound mastering engineers, credited on a wide range of US pressings. |
Initials get reused across studios and decades, so a match on initials alone isn't proof — treat it as a lead worth confirming against a discography or Discogs entry, not a verdict on its own.
Hand-etched marks were scratched into the lacquer by the cutting engineer during mastering, so they look irregular — like handwriting. Machine-stamped marks were impressed later during pressing setup and look uniform and typeset. Both are equally legitimate; the difference is only which stage of production added them.
A low take or stamper number generally points to an earlier pressing, but high-demand releases often ran several stampers in parallel on different presses at once. A "1A" and a "1M" pressed on the same day are both legitimately first-run copies — the letter identifies the tool used, not a strict release order.
Beyond engineer initials, many plants stamped their own small logo or symbol into the dead wax — stars, geometric marks, or simple letter codes identifying which factory pressed the disc. These varied enormously by country and era, so they're best looked up per-label rather than memorised as a fixed list.
Transcribe the matrix code exactly as etched, dashes and all, and search it against the release's Discogs entry. Discogs' own "Matrix / Runout" field exists precisely so collectors can compare codes and confirm which specific pressing they're holding.