What's with folks not listing the diameter of their coins?

[Anaximander]

Neat idea, @akeady. No decimals, but practical.  Where on earth does one come up with such a thing, these days? Did you get that in the 1980s? That looks so pre-information age!

[Nerosmyfavorite68]

It's annoying, as I don't have a caliper.  I do, however, have a couple of cheap rulers.

Where does one get a digital caliper (and decent scale)?

What's worse is if all the information is there and they still get the attribution wrong.  I bought a 35 mm. 'Constans II' (which was clearly Phocas).

[akeady]

1 hour ago, Anaximander said:

Neat idea, @akeady. No decimals, but practical.  Where on earth does one come up with such a thing, these days? Did you get that in the 1980s? That looks so pre-information age!

It does look a bit old-school, literally 😄   I think I got mine in Tesco, but there are lots of them on Amazon:

https://www.amazon.com/s?k=circle+template&crid=1W6YL5YZK14G6&sprefix=circle+template%2Caps%2C183&ref=nb_sb_noss_1

Yes - no fractions of a mm, but if the coin is off-circular, there's no point in quoting diameters to microns!

ATB,
Aidan.

Edited June 5 by akeady

[Valentinian]

The purpose of stating the diameter is to convey information. What information does a viewer want? What method is most helpful?

Obvious, buyers want to know "how big" it is. If a coin is close to round, one number will serve. If not round, it is easy with a caliper
https://www.amazon.com/Digital-Caliper-Sangabery-inches-Vernier/dp/B07VSVMWTJ/ref
to find the "maximum" diameter and "minimum" diameter.  Even a ruler can do the job, close enough, anyway:
https://www.amazon.com/Straight-Flexible-Suitable-Measuring-Centimeter/dp/B09B6SZRKR/ref
State both the maximum and the minimum, say in the form "22-19 mm," and the size of the coin is clear to the reader. 

The maximum alone can be slightly misleading if the coin has, say, a sprue or irregular shape. Weights are useful, as others have noted, for detection of counterfeits and clipping. But, that is a different level of information. Diameters tell what most of us want to know, "How big is it?"
 

[expat]

If I need to add the diameter because the auction info is missing, this comes in handy. It is the opening page to all my albums. If the coin is generally round, then the round number will suffice. If the coin is irregular you simply match the edges with the circles and record twq dimensions, such as 23/26.

[Julius Germanicus]

One cannot tell a mid 3rd century Roman As from a Sestertius from the weight (if it is, let´s say, 12 grams), but certainly from the diameter of the design.

[Heliodromus]

On 6/5/2024 at 10:52 AM, Valentinian said:

Diameters tell what most of us want to know, "How big is it?"

I think that depends if it's a type that you're familiar with or not. If you already know the type/issue, then you know the approximate size, and by looking at a photo can see whether a particular specimen is on a normal or under/over-sized flan.

For me, for Constantinian LRBs, the reason a measurement is occasionally useful is to tell what issue is it from, or occasionally what denomination it is (if no weight is stated and denomination is in question), so I'm not really asking "how big is it", but rather "what is it?".

For example, at the London mint c.307 AD there was a coinage reform and reduction from 1/40lb to 1/48lb (nominal 8.22g to 6.85g), and at least one type, GENIO POP ROM, was issued at both standards. Unfortunately the weight is not a useful way to tell them apart since lax weight control means than coins closer to 8.22g can in fact be from the later light standard and vice versa. This is a real practical issue - I've bought a few coins based on weight only to discover in hand that it was not the issue I was expecting.

However, as noted above, while flan weight & size was poorly controlled, dies were well controlled, so one really wants to measure the die not the flan. It turns out that the diameter of the beaded border (aka PRD - pearl ring diameter) on LRBs was well controlled as part of die engraving (they would inscribe a circle of the requisite diameter, then punch the border on that circle), so Bastien refers to these 1/40lb and 1/48lb standards by PRD instead (24mm vs 23mm). It's not just a matter of identifying what you are buying, but also a research question to identify when new types were introduced.

Many times when PRD is of interest, but not given (as is typical) then I'll load the coin into GIMP (Photoshop) and measure the PRD relative to the flan size and calculate the PRD based on a stated flan diameter, but garbage-in garbage-out applies and auction houses aren't always providing an accurate maximum diameter. On occasion I've asked a seller to either measure the PRD or take a photo with a ruler in it so that I can measure it myself in GIMP.

 

Edited June 7 by Heliodromus

[Valentinian]

3 hours ago, Heliodromus said:

I think that depends if it's a type that you're familiar with or not.

True. But, there are many different levels of collector and not all are familiar with all the sizes of all the types the vast field of ancient numismatics. I think it is kind to the reader or potential buyer to give the diameter automatically. 

I have late Roman soldier-spearing-fallen-horseman coins from 24 mm down to 16 mm. In that series it is obvious that the size should be given or else the viewer can be misled. In many other cases the size is obvious to those of us who have been collecting for years, but long-time collectors are not the only audience for the information. What is the value in not giving the diameter? 


 

[Alegandron]

My YAP Coin is 8'2" (2489.2 mm)

[hotwheelsearl]

17 hours ago, Valentinian said:

True. But, there are many different levels of collector and not all are familiar with all the sizes of all the types the vast field of ancient numismatics. I think it is kind to the reader or potential buyer to give the diameter automatically. 

I have late Roman soldier-spearing-fallen-horseman coins from 24 mm down to 16 mm. In that series it is obvious that the size should be given or else the viewer can be misled. In many other cases the size is obvious to those of us who have been collecting for years, but long-time collectors are not the only audience for the information. What is the value in not giving the diameter? 


 

I like seeing all the discussion about the reasonings, and how scientific folks want to get for diameter. There is no value in NOT stating an approximate diameter, there is only a gain. I guess I suppose one has to determine if they are willing to expend the extra few seconds to measure a coin, or not.

I for one agree with several statements made above, where weight is not a very good metric for coin type. When weight standards were lax, when you have similar coins made of billon, or silver, or silver washed whatever, then the weights vary dramatically, but the diameter doesnt.

[Alegandron]

I collect thick coinage also, so I like to add a 4th dimension of measure (Weight, H x W x THICKNESS)

 

RR Aes Grave Anon 280-276 BCE Triens 46mm 90.3g 9.3mm thick Tbolt-Dolphin Rome Crawford 14-3 T Vecchi 3

 

Carthage 201-175 BC Æ 15 Shekels 45 mm 7.5 mm thick. 102g WreathTanit Horse uraeus above. MAA 104 SNG Cop 400 RARE

[-monolith-]

On 6/4/2024 at 2:26 PM, hotwheelsearl said:

I am not trying to call anybody out, but I have noticed an odd trend where some collectors of what I could consider the more "advanced" variety tend never to list the diameter of their coins.

They will post a picture, have a slew of information, and then just the weight. Considering that the composition of coins varied hugely, saying that a coin is "4.3g" means almost nothing. I want diameters, gosh dern it. Oddly enough, those of the more "amateur" variety tend to list weight AND diameter. Why?

I can honestly say that I don't list the weight or dimensions for most of my coins simply because I haven't verified them yet and I don't trust the auction listing. If I'm asking for an opinion, help identifying, or something similar then I will post the information provided from the auction. But I agree, size, weight, and metal content are very important. It also depends on the reason your posting a coin. In most instances it's collectors just having fun posting their coins that have depictions of bulls or sacrifices, etc. while other post are more serious and educational. Eventually, when I have time, I will go thru my collection and verify the dimensions, weights, and properly photograph them so I can provide a detailed data sheet for each coin like this:

Edited August 27 by -monolith-

[rasiel]

On 8/25/2024 at 12:48 PM, -monolith- said:

I can honestly say that I don't list the weight or dimensions for most of my coins simply because I haven't verified them yet and I don't trust the auction listing. ...

I'm in the same boat! To me the weight is sine qua non. It's unforgivable for an auctioneer to not list it. It screams "our cataloguers are minimum wage earners". A diameter on the other hand is nice to have but doesn't mean much to me. I can't think of a single time a diameter played any bearing on whether I bid or not. I do, however, think 40mm Justinian folles are cool and you wouldn't know by just pic and weight alone. Then again, it must be said I focus solely on Roman Imperial and Byzantine coinage so diameter might well be crucial for other periods.

A hidden benefit of listing weights, and to a lesser extent diameter, is that it aids in tracking down provenance. You might have hundreds of a given coin type in a database which you can whittle down to a handful of potential coins with a search that is plus/minus 0.1g. Because I like to take things to an extreme, I use a scale that is good to within a tenth of a milligram. Overkill, yes, but great to mark a coin with what basically becomes a unique fingerprint even within a sea of me-too coins like solidi whose weights are often usually 4.45±0.05g.

Back in the day when I scraped by as a numismatist I used to certify coins. Here's one of those certs showing how much of a stickler I am when it comes to data precision 

Rasiel

 

[hotwheelsearl]

I like giving both because it’s easy and approximate. Especially for LRBs that run the gamut from 13 to 18mm, often with similar weights.

for example, I have a variety of CONSTANTINOPOLIS coins that all look similar but some are tiny and some are not.

when distinguishing between “AE3” and “AE4,” it gets confusing to the point where some are listed as “AE3/4”