Why do so many auction descriptions include the weight but omit the diameter?

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The reason is that auctions are all about making profit and often a lot of value in a coin is tied to its metallic composition. When it comes to giving the weight, the purpose in doing so is to denote its value based on that (especially when it comes to silver and gold) wherein the diameter itself is not seen as relevant. So there you have it: a narrow focus on the desire for profit based largely on a coin's metallic composition.

Edited to add: I noticed this thread in the "Recent Topics" column and did not observe that it was posted in the "Ancient Coins" sub forum until after my post was made. I would say that generally speaking, my post is relevant more so in a broader context wherein modern coins are in the mix of discussion.

 

I don't believe that the metal value is important for ancient coins, but e.g. I wouldn't buy a tetradrachm without knowing the exact weight. Knowing the weight is important, and therefore, yes, they would lose the profit if they also left the weight out.
Yet I don't understand why some sellers omit the diameter. Maybe they don't want buyers to realize how small a coin is in reality.

 

I don't think any coins other than bullion are tied to their metallic composition.

I am annoyed by the lack of diameter as well. I just don't know all the different denominations from all the different cultures across all the different times, I'm too much of a generalist collector. So, I feel you pain @lordmarcovan .

 

That irks me, too.

 

thank you so much for asking this exact question! I often wonder this too, but thought that it was common knowledge and its stupid to ask.... Even though for ancients the diameter is within a certain range, if i could chose i would always go for larger specimen than a smaller one. I put the coins in a display trays and dont weight lift them or something, so i want to know the diameter. The view is a bit better when the coin is a few milimeter bigger, right? (i get the importance of weight, of course)

 

I only recently started recording diameters on coins I buy. No that we see mostly enlarged images online, that statistic is more important than when we usually saw actual size images in printed catalogs. Two coins being struck without a collar (all ancients) will vary in diameter according to how hard the hammerman hit the dies. While weights vary, they were more likely to convey needed information until this recent change to online imagery making it hard to tell a 20mm coin from a 30mm one in a photo.

 

Posting the diameter is fine but it can be a problem when the coin is shall we say less than round. which axis do you use? Or like on this guy where do you start?
Derrones Dodekadrachm 475-465 B.C. HGC 279

 

For my own notes, when the flan is oddly shaped, I go from the widest diameter. In such a case as the dodekadrachm you posted, I would include in my notes something about the flan shape and include the narrowest measurements as well.

 

Thank you @lordmarcovan, this bothers me too and I have been meaning to make this exact thread.
Maybe if we complain loud enough they will take notice.

Size DOES matter, it matters an awful lot.

 

Having worked in Quality Control for 25 years (the machine tool industry) I can attest the only correct way to measure an outer diameter is by maximum dimension, such as a coin. By contrast, the only correct way to measure an inner diameter is using the smallest diameter. The weight of a coin is far more important than its diameter since very few ancient coins are round. You can calculate roundness by using the largest & smallest diameter of an object such as a coin.

 

I have historically only weighed my coins but in the last couple of years have been trying to record the maximal diameter and the die axis.

In some cases I record both the maximum and minimum diameters.

Probus

Obv:– IMP C M AVR PROBVS AVG, Radiate cuirassed bust right
Rev:– MARS VICTOR, Mars walking right, holding spear and trophy.
Minted in Lugdunum (II in exe) Emission 3, Officina 2. November – December A.D. 276
Reference:– Cohen 337. Bastien 179. RIC 37 Bust type F

4.80 gms, 23.43mm x 25.20mm

 

I only record minimum diameter when it is at last 2mm less than the maximum. I am considering making a measuring scale that would allow placing the coin in a series of holes that would tell which fit. I see no reason for fractions of millimeters since there is so much difference to be had when you are selecting the maximum to measure.

 

For measuring diameters I use one of these:



The first hole the coin fits through (going in order of increasing diameter) is the diameter I record. I don't rotate the coin to squeeze it through, so get the longest diameter - if a coin is very oblong, it could be rotated and fit through a smaller hole - you get what I mean!

ATB,
Aidan.