Saw a question about what a "filled in" Mintmark is. They wanted to know what it is and how it happens. I wasn't quite sure how to answer that question. I was thinking "die chip" though. Help wanted please... ( Daxter and I will be waiting for answers....
Definitely a Die Chip. But it also could be displaced metal caused by circulation wear and tear. I always see "Filled in mint marks" listed on eBay. Sellers think there's a premium for the issue when there really shouldn't be! Just look at these ludicrous listings..
I seem to see them fairly routinely on proof coins. I think it is likely more a result of die polishing though I really don't know. A Denver mint on some JFK halves that I have seen look little more than a blob.
If you are talking about D MM it is the center post that breaks from the die face, it is definitely a die break.
…AND it is the same for the P mint mark. The center post breaks off for both and extra metal fills in during strike creating die chips (IDB) and blobby mint marks. The premium comes in (imo) on proofs because it slips by quality control, ends up getting into OGP and into collector hands. @paddyman98 makes a good point about circulation damage ‘cuz that is definitely possible on business strikes and can be impossible to tell the difference. If I had a BS and saw wear elsewhere I would call it a toss-up. Conversely, If I had a proof I would conclude a die post break only…Spark
A filled in mint mark is mostly caused by a break on the die. When a die breaks or cracks the metal flows into that space and creates a blob. The size of the blob is based on how much the die is broken. A coin that has circulated and has a worn mint mark can also lead to a filled die. Any coin with a P or a D mint mark is more likely to become a blob but the S will do it as well. The P and D are filled in but the S isn’t so it takes longer.
The die failure described in the OP is typically called a "die chip". The term "die break" is more general and all-inclusive and can also include die cracks. Die chips usually occur where there is a stress concentrator at a small cross-section area of the raised portion of the die. This is most often seen at letters and numbers and is more often seen in small coins where the devices and thus the cross-sections are uniformly smaller and thus the stress concentration higher. These die chips were practically ubiquitous in the early decades of the mint when the die steel was sub-par compared to today. These chips are critical to determining die state and emission order. I collect capped bust half dimes (1829-1837) by die marriage (124 collectible marriages and remarriages) and die chips appear everywhere in this coinage. Below are some of the most commonly see die chips in this series. Note that the die chips occur at sharp corners and at isolated "posts". I've only shown reverse chips but typical die chips on the obverses occur mostly in the loops of the 8 and 3 in the date.
