Ranjit Singh 1851 Amritsar mint Rupee

Started by 1rupee, December 11, 2024, 05:54:03 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

1rupee

I have been going through this category - looking at Indish stuff - and find some fascinating posts. Contemporary fakes, copper peeping out of silver plate etc.

Anyways, here is a Ranjit Singh Amritsar Rupee. Picture doesnt do justice, it is sharp minty. But has various coppery dots seen under magnification. Diameter is around 22mm, other details as in pic.

On the edge, there is no seam, but two light punch marks. Much lighter than normal dots seen on Indian coins.

Would welcome comments


1rupee

btw I dont think this is a fake. But the coppery dots... how/why?

Interesting observation is those coppery revelations show not at highest ridges, but just beside, in the shade, fully protected by the ridge.Cant be wear/tear


Figleaf

Are the two punch marks on the edge right opposite each other?

Peter
An unidentified coin is a piece of metal. An identified coin is a piece of history.

JohnI

One possibility for the copper, and I am sure there are several is as follows.

If silver is cleaned with thiourea (e.g. silver dip) and there is a lot of copper present, then copper sulphate can form on the surface, making the silver black - as happened with the two older coins you used silver dip on.

A source of copper on the surface is the leaching out of copper from the silver, which is a cause of silver going black as it tones. If a coin was buried, it is possible for the copper compounds to disperse into the soil. If the coin is stored then there is a high probability that the copper compounds would not disperse. Copper leaching out would result in the surface having a higher silver content than the metal underneath. Your surface spectrometry results do indicate a high level of silver on the surface (i.e. that copper has leached out of the surface).

If electrolysis is used to clean silver with significant copper sulphate on the surface, the copper sulphate on the surface, when converted to copper, will leave the silver looking like copper. If the silver has been subjected to an abrasive method (e.g. normal wear, baking soda and soap),the result could be copper surfaces in crevices. The abrasive methods can happen before or after electrolysis.


Regards;



John
   

1rupee

@Figleaf the dots are beside each other

@JohnI I havent cleaned this coin, but somebody before me would certainly have. Thanks for your explanation, had to read it 3 times to understand all you mention :)

So:
  • if coin has high copper content, thiourea can cause instant blackening as I observed on 2 ancient/antique coins (5-6% Cu)
  • on modern coins with high copper content, like sterling of cupro-nickel I havent seen phenomenon though
  • I was surprised by the high Ag content of silver in the Mahmudi. It is supposed to be billon, your leeching explanation makes sense


JohnI

From what I understand the silver content of Indian rupees of the period is about 91.5%. The German East Africa coins are about the same - 91.7%. Although technically billion, this silver level is not far from stirling silver. So it should be OK with thiourea.

In other words, the issue would not be the silver content of the coin, but the amount of copper that has come out of the silver as corrosion products - tone or deposit. So in effect the problem is the amount of free copper to react with the thiourea and turn the silver black.

Two factors that can make older coins different from newer coins are:-

Time - the longer the toning/corrosion process takes place, the more copper that will leach out.
Acid levels - higher acid level will give more copper leaching. For example older coins could have been stored in PVC envelopes.
 

Regards;


John

1rupee


krishna

Quote from: 1rupee on December 11, 2024, 04:42:55 PM@Figleaf the dots are beside each other

@JohnI I havent cleaned this coin, but somebody before me would certainly have. Thanks for your explanation, had to read it 3 times to understand all you mention :)

So:
  • if coin has high copper content, thiourea can cause instant blackening as I observed on 2 ancient/antique coins (5-6% Cu)
  • on modern coins with high copper content, like sterling of cupro-nickel I havent seen phenomenon though
  • I was surprised by the high Ag content of silver in the Mahmudi. It is supposed to be billon, your leeching explanation makes sense



also depends on the alloying techniques, copper has a higher melting point than silver, thus some copper clumps may have inadvertently formed if the alloying was not done properly, causing the copper clump to react faster than silver (as per reactivity series of metals)

the marks on the side, seem like test marks, as indicated by @Figleaf
so it may be assumed that your coin is genuine, with some manufacturing defects
 

1rupee

@krishna interesting point on copper having higher melting point than silver - makes sense.