Great advice.
The metrics I use relate to how often a coin
type appears on the international markets
Once a decade or less, and it is of major importance when one appears -
excessively rareOnce every two or three years and there's a buzz about the sale -
extremely rareAbout once a year; in a given two or three month catalog/internet lookahead there might be none or one -
very rareSeveral times a year; if one searches one can usually find an example or two in a 3 month interval -
rareOne or two examples now, in an internet
search and/or including upcoming
auctions -
scarceA range of examples are available at fixed-price and in upcoming
auctions -
commonMultiple examples are available at fixed-price and in upcoming
auctions -
very commonYou have to wade through bucketfuls of this
type to find an interesting coin -
extremely common(this is calibrated around
Roman Republican silver which is a popular collecting
area where very
rare coins are virtually guaranteed to get listed in a major
auction: for less popular areas such as
Republican bronzes, even genuinely
rare types are often ignored by sellers and languish in pick-boxes; thus frequency of appearance in proper
auctions is less than the
rarity justifies)
I have written some words on the concept of
rarity here:
http://andrewmccabe.ancients.info/Auctions.html#jumpWarren Esty has written better words here:
http://esty.ancients.info/numis/rarity.htmlFrom
Warren's site: here is Glossary of
eBay terms (tongue in cheek):
"not in Sear" It is unlisted in Sear's book, so I can't give a
Sear number. (I
hope you think this makes it
rare and valuable.) [Of course,
RIC lists thousands of varieties not in
Sear, so it doesn't really mean much at all.]
"r2" or "very rare" RIC lists it as "r2" [This is almost meaningless for late
Roman coins.]
"Unlisted" I have only one book and its not in it.
"The first one I've seen" I've been collecting for a year, have almost no reference works, and have not yet seen this [although experienced collectors have seen 50 examples].
"Van Meter Value Band 2" A more-expensive
type. (I
hope you don't know that this late Roman copper
type has been pouring out of the Balkans since the iron-curtain came down [after
van Meter wrote
his book] and they immensely more common than they used to be and are going for 1/4 what they sold for when
van Meter wrote
his book.)
"unpublished" I have several of the major references and its not in them. [But most of them are 20 or more years old and who knows what has been published since then?]