Metallurgy Testing or Metrology Testing

So after a break of a few years the testing has restarted. Or perhaps the work carried on in the interim was commercial in confidence leading to the first stage of commercialisation of a new technique.

But we now move on to the first intensive testing of coin metallurgy with our new technical partner.

The are fundamental gaps in the knowledge base of Indian sub continent numismatics and, perhaps, in this area a rather large gap in the knowledge base almost everywhere. It becomes a matter of careful analysis of data available and then designing a series of tests that will be carried out in the strictest quality control measures at an appropriately qualified laboratory approved and recommended by the testing equipment manufacturer.

The first tests are always the most interesting especially we are at the limits of technology ore perhaps I should say when we are at the limits of what people generally believe are the limits of the technology.

The technology is high end XRF. I am still somewhat bemused at people who refuse either to use this technology or wilfully misunderstand its abilities and limitations. recently in a discussion a number of papers written in the 1990 were used as examples to express a complete reluctance to use the technology. Technology develops and so the methodology surrounding its correct use. Thankfully we are supported by the world's leading technology group in this as we move forward.

So we are testing under full quality control conditions the complete makeup of coins down to ppm.

What has this got to do with metrology of coins? Quite simply metrology is the scientific study of measurement. With numismatics we think that weight and diameter (of round coins) is sufficient however that is fine for base metal coins such as copper. However within a series of coins there is frequently a series of precious metal coins also issued. These are usually gold or silver (or perhaps a mixture of both). This presents a tri metallic series with gold normally being the most valuable followed by silver and then copper (and perhaps other base metals depending on the series). For a number of coin series we have a metal alloy called potin or billon. This is normally an alloy of silver and copper. So now we have four types of metals plus in the greater sub continent of India for much of the time we have humble money. Humble money was a unit of exchange that was perhaps cowrie shells, bitter almonds or similar. It was a known medium of exchange at the base level and used instead of pure barter.

So we have here a complete series that can be exchanged. Coins (or humble money) of lesser value can be traded upwards and coins of a higher value can be exchanged for a number of lower value coins. Today this somewhat simple because in general the 'value" of the coin is shown on it and we know precisely what the various exchange rates are.

This then brings us to another vital point in metrology. What is the purity of the metal in the precious metal coins? Without going into a long winded discussion the purity (fineness) of the precious metal can be varied during manufacture so it is of the utmost importance that we know this because it affects the rates of exchange between the metals (in this case the coins) . Where the value of the coins, especially the precious metal coins, is a direct reflection of the purity of the metal then for the purposes of metrology we need to ascertain the purity of the metal. This can now be done extremely accurately, without damage to the coin and very quickly (noting standard quality control measures).

Unfortunately a great deal of research has been completed on finding out the weight of the fundamental unit of much of the greater sub continent, the rati. The rati is a seed and its weight varies from district to district and season to season. Over time with the transience of empires and changing standards and sizes of coins the actual weight of a rati at any time in numismatics is not essentially important.

For further discussions on this point and minting please review.


1. The weight of coins (in any units) is highly important. For modern work grams should be utilised. The units of weight perceived to be in use at the time the coins were minted is unimportant.

2. The inter relationship of weights within the same series is highly important.

3. The fineness/purity of the metals used to make coins is highly important as are any changes within the fineness within series and over time. Fundamentally a coin can reduce in weight and increase in fineness and not change its exchange value. A coin can also increase in weight and reduce in fineness and still hold the same exchange value.

4. The exchange rates between metals is important. This defines to a major extent the exchange rate between coins of different weights and different metals. That is to say how many copper coins of weight X are needed to "buy" one silver coin of the weight within the silver coin series. Different coin metals often have different weights in their series compared to other metals.

5. It is now possible to simply and accurately determine the precious metal content in coins without any damage provided that the techniques are fully understood and adequate quality control is maintained at all times noting the requirements of the equipment being used. Highly advanced and accurate equipment is highly portable.

So now highly accurate measuring equipment is available to complete the metrology puzzle without damaging the coins. The possibilities when used correctly become almost endless in numismatics.


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