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 Replies: 9 / Views: 1,043 |
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Pillar of the Community
 United Kingdom
1168 Posts |
I put a couple of uncleaned Roman coins in de-ionised water, in preparation for a light cleaning. After a couple of days the coin in the middle of the dish seemed to be exuding a white substance, powdery in appearance. It looks to be flowing over the bottom of the dish. I have not seen anything like this before, and the water does not taste salty. Can anyone tell me what is causing this reaction? Thanks, Jim  |
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Pillar of the Community
United States
5825 Posts |
My guess is that the coin was struck in zinc.
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Pillar of the Community
 United Kingdom
1168 Posts |
I hadn't thought of that. Thanks @kanga.
Jim
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Bedrock of the Community
Australia
21786 Posts |
I don't know of any ancient coin made from zinc, except that the Chinese made a few cast cash coins from this metal.
The Romans did, however make sestertii from orichalcum, (similar to brass), which is an alloy of copper and zinc.
If the coin pictured was of orichalcum, it was most probably of Roman colonial origin, due to it's size as shown here. The Roman Imperial coins of orichalcum were the sestertius and the dupondius, which were much larger and heavier.
I have never fooled around to test the sestertii and dupondii that I have, with tap water immersion, and I see no reason why I need to now.
But I do not suspect that there would be any short term chemical activity. Not enough zinc in the alloy - much the same as modern brass, which is occasionally used for domestic water plumbing.
In the long very term, (years), a very slow reaction known to plumbers as 'de zincifation' can take place in adverse circumstances.
Edited by sel_69l
08/26/2020 01:38 am
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Pillar of the Community
United States
3433 Posts |
Romans had a very imperfect understanding of zinc
It was used to produce the 'orichalcum' but it was done through a complicated process where the zinc became alloyed with copper to produce a golden colored form of brass
But refining the zinc was beyond their technology
What is the coin by the way ? I can see a portrait
Was it found in Britain ?
I suspect it must be something in the oxidized surface
It looks like it may be concentrated in spots on the surface
Perhaps it came from fertilizers used on a farmers field ?
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Pillar of the Community
United Kingdom
1168 Posts |
Thanks for the replies, and I now know how zinc reacts in water. Quote:
What is the coin by the way ? I can see a portrait. Was it found in Britain ? The coin has been in a box of uncleaned and unidentifiable coins. I have had some of them for so long that I don't remember where they originally came from. Now that the coin has been dried, there is very little detail to be seen on the surface. On what looks like the obverse, there does appear to be a very degraded portrait. There seems to be an "A" and an "N" around the forehead and eye level, and a small star to the right of the "N". I can't make anything else out. It looks to be too far gone to even guess what it might be. Diameter: 16 mm. Weight: 3.1 gr.  On the reverse, I can make out an "O" and an "N" in the exergue. In the main field there appears to be a standing figure to the left, and two legs (?) to the right with an inverted V above.  |
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Pillar of the Community
United States
3433 Posts |
Exergue reads LON
That's the easy part !
I suspect that the obverse needs to be rotated slightly (45 degrees) clockwise
I believe the portrait is of the "Usurper" Carausius
With some patience we will crack this nut
Edited by FVRIVS RVFVS
08/26/2020 4:48 pm
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Pillar of the Community
United States
3433 Posts |
Hmmmm
I thought my memory had Carausius (or Allectus) using the LON
But it appears not !
Still I am fairly sure you have an LON
So now we know it dates post Allectus
It may be an unofficial issue of Constantine
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Pillar of the Community
United Kingdom
1168 Posts |
I'll never know how you manage to provide so much information on such a depleted coin @FVRIVS RVFVS. It can actually have a label now, thank you very much. I have attached the image rotated, though it still doesn't mean much to my eyes.   |
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Pillar of the Community
United States
3433 Posts |
Not much of a label besides the 3 letters
I can make out a profile of sorts
Eye nose chin
But whose ?
There are others here who are much better at these types than I
The 16mm flan is small
But the 3.1 grams is actually fairly robust for an LRB and it surely has lost a few tenths from corrosion
I am sure else here will have a better idea
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Replies: 9 / Views: 1,043 |
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Posted 08/25/2020 8:37 pm
