Indo-Portuguese 1/2 Tanga - Query

[amit79]

I recently acquired a number of Half Tanga coins of Carlos I - MCMI (1901) and MCMIII (1903). I noticed that some of these coins were heavier than the 12.7 grams mentioned in Numista (https://en.numista.com/catalogue/pieces11760.html) - see pictures 2 & 3 - 13.14 & 13.17 grams.

Normally, a coin so far out of weight should be fake. However, among my other coins, I found the same issue with a 1903 coin (fourth picture) - this coin was 12.97 grams and is very worn out (picture 4), so in original condition, may have been 13.15 grams. Also, from this lot of very worn out coins, I found Half Tanga coins of varying thickness (picture 5). All these coins are heavily worn out, so in my opinion, unlikely to be fake.

I checked this anomaly with two different dealers (not the one I bought from), both of whom said that weight and thickness variation are due to change in year/mint etc. Both have much practical experience of coins, but little formal education and couldn't direct me to any books/formal source.

My personal sense is that these coins were minted in a small number (800,000) and in a relatively smaller mint (Lisbon) with a non-precious metal - so it is possible that quality control was not as stringent as it is for British Indian coins or silver coins - of which over 100 million were minted in some years. Accounting for this variation.

Any additional information/perspective will be welcome.

[Figleaf]

Usually, the weights in Numista are observed weights, but in this case, they seem to have used the legal weight, which is indeed 12.7 grams (source: Moedas Portugueses by Alberto Gomes)

Your four coins form a very small population, so all conclusions are tentative, but here goes. The range of weights your scales report is from 12.51 to 13.17. The official weight is within that range. When the law establishes the weight of a coin, it also gives some wiggle room, like a percentage a certain number of coins may be lighter or heavier, the remedy. The usual remedy depends on the technology used to produce the flans. For this period, I would consider a remedy of 1 - 2% on 100 coins normal.

The average weight of your coins is 12.95 grams, which is slightly less than 2% heavier.

However, the heaviest of your coins is practically 3.7% overweight. That amounts to only 0.47 grams though, a weight difference that is imperceptible to humans. Looking at your edge view picture, I think I see very slight differences in thickness between the coins. Without the enlargement and knowing about the weights I would probably not have noticed this. In an economy without vending machines (1903!) this difference would have gone unnoticed. Even today, only the more sophisticated vending machines check for thickness. In other words, even your heaviest coin was fit for circulation.

I think we may conclude that the rolling machines in the mint that produced these coins (Lisbon?) were not as precise as they are today, but precise enough to get 100 random coins within the remedy. Therefore, unless your scales need re-calibration, the weights of your coins are acceptable.

Peter

[amit79]

Thank you for the detailed response. This was very helpful.

One clarification though:
I have ~25 coins of this type, 3 were over the 'spec' weight of 12.7 - I pictured all the three. The others were all in 12.2-12.6 range.

I spoke to yet another dealer selling these in bulk - he concurred, that there are some differences in die/thickness of this variety. So far, I have dealt mostly with British Indian coins, which are more finely machined, so was completely unused to such a divergence. My concern was that the overweight coins may be fakes, but that seems less likely now. Also, a big lesson on how to use information on Numista. Once again, many thanks.