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Author Topic: Please I need help with Ptolemy VI tetradrachm!  (Read 1604 times)

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Offline Basileus Nikephoros Antialcidas

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Please I need help with Ptolemy VI tetradrachm!
« on: February 12, 2019, 08:46:06 am »
Just got this Ptolemy VI tetradrachm witch is as you can see quite beautiful. NGC encapsulated and generally everything seems perfect. The one thing I can't really understand is there are some brown spots on it (around the mouth and nose, behind the hair and at 2 o clock. They don't seam like bronze at all, they seem like someone dropped some melted chocolate on it. They look like brown clay has stuck on these parts. That's the best way to describe it. Please help me I need to know what this is.
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Offline Basileus Nikephoros Antialcidas

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #1 on: February 12, 2019, 05:17:19 pm »
One more photo
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Offline djmacdo

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #2 on: February 12, 2019, 06:43:18 pm »
The piece in the upper right obverse field is clearly a remnant of encrustation that his otherwise been cleaned off.  The others may be as well, but I cannot get a good look at them despite your excellent photographs.

Offline djmacdo

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #3 on: February 12, 2019, 06:45:07 pm »
We have seen this coin before--you were worried then about the odd seam at the upper right.  If the coin bothers you this much, you might want to submit to to someone to look over in person.

Offline Basileus Nikephoros Antialcidas

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #4 on: February 12, 2019, 07:52:55 pm »
We have seen this coin before--you were worried then about the odd seam at the upper right.  If the coin bothers you this much, you might want to submit to to someone to look over in person.
Thank you very much for your answer! No it doesn't really bother me anything. I am 22 years old less than a year on the hobby and trying to understand and learn as much as I can and always be as sure as  I can of what i have on my collection. I also always value an opinion from people who are veterans on the hobby! Also can you please explain what is a encrustation on coin? Is it normal for a tetradrachm from that period to have it and also is there any bronze on the alloy of these tetradrachms or are they completely silver? Also I have found an other tetradrachm on the internet with very similar look on the encrustations so for you to have a better look on how they look they look like the photo below in much lesser amount.
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Offline djmacdo

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #5 on: February 13, 2019, 08:22:47 am »
This second tetradrachm seems to have both encrustation on some indication that it may be plated--the corrosion before the face near the edge and the copper that seems to be showing through on the face.  These late Ptolemaic tetradrachms were rather debased, and the copper look may rather be due to the harsh scrubbing to which this coin seems to have been subject.

Offline PtolemAE

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #6 on: February 13, 2019, 02:51:39 pm »
This second tetradrachm seems to have both encrustation on some indication that it may be plated--the corrosion before the face near the edge and the copper that seems to be showing through on the face.  These late Ptolemaic tetradrachms were rather debased, and the copper look may rather be due to the harsh scrubbing to which this coin seems to have been subject.

The big chunk or flake that appears to be missing at the top of the head seems to show the metal underneath is 'silver' which doesn't look like a silver-plated copper core.  Some alloys can have surprising appearance when polished.  One large Ptolemaic 'bronze' drachm coin, worn and missing a big broken area, was partly sanded and polished to remove oxide and patina for an XRF test on a clean fresh metal surface.  The polished area had an unexpected silvery appearance. 

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #7 on: February 14, 2019, 05:36:33 pm »
Good observation--so probably not plated but the remnants of corrosion fooled me.

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #8 on: February 15, 2019, 12:51:46 pm »
Good observation--so probably not plated but the remnants of corrosion fooled me.

The Wikipedia chemistry experts describe two prominent oxides of copper - cuprous (red color, two copper per oxygen) and cupric (black color, one copper per oxygen).  We see what is likely the red oxide often encrusted on bronze coins.  Maybe this silver is so debased, or perhaps the copper not thoroughly mixed in the alloy, that the red oxide forms in some places where conditions favor that chemical reaction. 

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Re: Please I need help with Ptolemy VI tetradrachm!
« Reply #9 on: February 15, 2019, 03:06:42 pm »
Quote from: PtolemAE on February 15, 2019, 12:51:46 pm
Good observation--so probably not plated but the remnants of corrosion fooled me.

The Wikipedia chemistry experts describe two prominent oxides of copper - cuprous (red color, two copper per oxygen) and cupric (black color, one copper per oxygen).  We see what is likely the red oxide often encrusted on bronze coins.  Maybe this silver is so debased, or perhaps the copper not thoroughly mixed in the alloy, that the red oxide forms in some places where conditions favor that chemical reaction. 

Here are some pics of the broken coin mentioned earlier that got sanded down on part of the reverse to show the underlying bronze.  The largest part of the coin has a black and very dark green patina, possibly coated with some of the black copper oxide.  None of the red oxide has occurred on this one.  The coin's large missing broken chunk void (clearly the broken area is old, maybe caused when it was struck or dropped on its edge long ago) made it a good candidate to donate its body to science.  Ptolemaic bronze drachm, Tyre mint, Sv 1126, ca 210 BC.

First pic is the coin a few years after the patina on part of the reverse (left edge about 9 o'clock) was abrasively removed.  It just sat in a box without much attention since the XRF testing.  The bronze-ish color seems to have returned perhaps due to oxidation.

Second pic is with the abraded area freshly cleaned/sanded off again.  The color is similar in that area now, but lighter.

Third pic is the freshly abraded area tipped back a bit and it looks quite 'silvery' when it reflects light at a different angle. 

Pretty interesting to see in hand just what freshly cleaned 2200-year-old coinage bronze actually looks like.



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