Enter your observations
Use measurements you can verify. Unknown or unreadable details can be left unspecified where the tool allows it.
Diamond-code entries
Choose the period/code table based on the mark’s documented style. If the code letters are illegible, do not guess: leave the uncertain part unselected where possible.
Ready when you are
Your results will appear here without reloading this page.
How to use this tool
- Photograph or transcribe the complete diamond, including the day numeral, month letter, year letter, and any Roman numeral.
- Select the early or late code table based on the mark’s layout; do not choose a period merely to force a desired date.
- Enter only symbols you can read, then note any ambiguity shown by the decoder.
- Compare the result with a reliable mark reference and the object’s other evidence.
What the result means
The British diamond registration-mark system was used from 1842 to 1883. The year-letter sequences are non-alphabetical and split into two periods: 1842–1867 and 1868–1883. Month letters follow a separate code list, and some combinations have documented exceptions.
The output is a registration-date clue. It does not prove that the marked object was made on that day: marks can be misread, copied, or applied in ways that need specialist context. Class numerals give a broad category such as glass, ceramic, metal, or wood, not a maker identity.
Limits and good practice
A blurred or partly hidden diamond may support more than one reading. This decoder covers the common published code tables and calls out several special cases, but it is not a substitute for comparing the mark shape, orientation, registration record, and object history. If the letter is uncertain, test each plausible reading separately and retain the alternatives.
References and further research
Frequently asked questions
Does the decoded date prove when this pot was made?
No. It points to the registration date encoded by the mark. Manufacturing, marking, or later copying can require separate evidence.
Why do I need to choose early or late code period?
The year-letter sequences changed in 1868, and the same letter can mean different years in the two tables.
What if one letter is hard to read?
Do not force a single answer. Test the plausible letter readings separately, photograph the whole mark, and document the alternatives.
What does the Roman numeral mean?
It denotes a broad registered-design class. It is not a date code or a maker’s name.
Are the exception dates important?
Yes. Some year/month combinations have documented special uses; a simple lookup can be misleading if those are ignored.
Can a copied diamond mark be detected by this tool?
No. A coherent code can be copied. Compare construction, provenance, style, and specialist reference evidence independently.