Oxidization - please explain

[superflex]

Hi guys,

I recently brought this coin that had apparent damage caused by being fused with an iron object causing oxidization to the nose area on Athena's bust. size 26mm and weight 17.1grams.

I have two questions:

First what is oxidization and are there different degrees of it ?

Online searches show it usually is caused by a loss of electrons, in case of coins where they may be leaning on other objects. On other coins found online apparent oxidization has caused a sort of less sharp image on a coin. Here it is almost a squashed effect?

Secondly how much does it effect a coins value?

I know values and prices is discouraged, but this is a fairly commonly known coin. From a subjective perspective, does anyone have an opinion of what price range may be expected when such damage is present. If anyone is uncomfortable relating to this particular coin please just refer to another coin and how some similar damage caused by oxidization has effected the value of the coin.

Is it just a question of aesthetics and subjective appeal ? for example i saw a beautiful owl that i couldn't resist and i paid what i thought it was worth ?


Is this a case of oxidization ? or is it other wear and tear. I have attached a link to the same coin in the shop ?

https://www.forumancientcoins.com/catalog/roman-and-greek-coins.asp?param=59524q00.jpg&vpar=66&zpg=71591&fld=https://www.forumancientcoins.com/Coins2/

[Dino]

I don't know that it's oxidation.  The reverse of your tet has an obvious test cut that looks like it has been repaired.

The damage to the obverse, to me, looks like it is exactly under the test cut on the reverse.  It is not uncommon for a coin to get flattened or otherwise damaged on the other side when it is struck by a chisel to form a test cut.

Here's your coin realigned.  If you fold the image, you should get your coin, so the damage on the obverse looks to be caused by the test cut.

Also it has some significant scratches around the eye.  Probably from cleaning.

[Dino]

Here are three other coins currently for sale that show similar damage.  The photos on the left are untouched.  On the set of photos on the right, I've circled in yellow the damage on the obverse resulting from the pounding of the chisel on the other side when the test cut was created.

[Dino]

Here's another one where the test cut on the owl was repaired.  I saw this coin in hand at a coin show.  The repair wasn't really visible in-hand, but I thought the flattening of the obverse was a dead giveaway.  I looked at the coin under magnification and you could see the lines where the repair had been made right between the eyes of the owl, similar to yours.  The silver there was also a slightly different color.  You can see that a bit in the photo below.  Very deceptive though.  Dealer stated he was unaware of the repair until we looked at the coin under magnification.

[superflex]

Thanks Dino,

So what is a test cut, what is its purpose ?  i have never heard of that before. Why would someone try to repair the coin only to damage it more?

was this repair modern or ancient ?

anyone else on oxidization point?  

[Salem Alshdaifat]

The test cut is to check if the coin is silver all the way, or it is just plated bronze, it that time many bronze plated coins were in the market (fake money), so people start to test cut the coins to be sure it is really worth the weight in silver.
best.
Salem Alshdaifat

[Dino]

Thanks Dino,

So what is a test cut, what is its purpose ?  i have never heard of that before.

As noted by Salem, one (if not the primary) purpose of a test cut is to ensure that a coin is solid silver.  The value of a coin was based on its weight in silver.  Ancient forgers would make coins with a bronze core, plate them in silver and try to pass them off as the real thing.  Those ancient forgeries are known as fourees.  I've posted photos from Reid Goldsborough's page showing a fouree.  A cut on a fourree would cut through the silver and expose the bronze core of the ancient counterfeit.  Here's a link to Reid's page if you want to learn more:

http://counterfeitcoins.reidgold.com/fourrees.html

Why would someone try to repair the coin only to damage it more?

The damage was done when the chisel struck the coin creating the test cut on the other side.  The repair is the blob of metal you see between the owl's eyes.

was this repair modern or ancient ?

Can't say positively, but I would assume with a fairly high degree of confidence that it's relatively modern by a seller or collector trying to improve the appearance of the coin.  Not sure why an ancient would want to fill in a test cut which proves the coin is solid.

[Joe Sermarini]

Can't say positively, but I would assume with a fairly high degree of confidence that it's relatively modern by a seller or collector trying to improve the appearance of the coin.  Not sure why an ancient would want to fill in a test cut which proves the coin is solid.

I think we can say positively the "repair" is modern.

[superflex]

Thank you all for sharing your knowledge, hadn't even heard of a test cut until today   

So in what way may a test cut effect a coins value ? How is a coin rated eg VF if there is a test cut ?


Can anyone then explain what a coin effected by oxidization would look like then ?

[Dino]

So in what way may a test cut effect a coins value ? How is a coin rated eg VF if there is a test cut ?

How much does a test cut affect value?  Significantly.  I don't think you can put a dollar or even percentage on it, because it depends on:

1.  the condition and grade of the coin (I think that on a percentage basis, a test cut affects price of a coin in great condition more than a test cut on a coin that costs less because of condition, centering, etc.).

2.  the location of the test cut and how much it detracts from the eye appeal of the coin.

I don't think there's any way to answer the question specifically.  I'd suggest checking acsearch.info and searching athens tetradrachms to get a sense of how much various coins have sold for based on condition, test cuts, etc.

Can anyone then explain what a coin effected by oxidization would look like then ?

Depends on the coin.  Oxidation on iron is generally rust.  On silver it's generally black tarnish or toning.  On copper it's generally that green patina that copper tends to take on.  Oxidation is basically the patina you see on coins.  Take a look at the members galleries here on this site and you'll see lots of different coins with lots of differrent patinas.  It's the oxidation that forms the patina.

Here's a link to the galleries in general:  https://www.forumancientcoins.com/gallery/index.php

Also below is a coin that has had the patina removed and is stripped to bare metal that has started to tone again just a little.  

Below that is a similar coin (same ruler any way) with the patina in tact.

By the way, patina on a coin is a good thing.  You can read several topics on that here.  CHeck out the uncleaned coins discussion for examples.

On edit:  I've added a third coin which also has had its patina stripped.  It's actually more representative of coins with patina removed than the first one in that you can see the pitting and corrosion on the coin that the patina was covering before it was removed.  Anyway, just explore this site and read and I think you'll learn a lot.

[superflex]

Thank you again, finding the time to read up is a challenge currently going through university doing a double degree, one of which is law. When I can I will keep exploring the site I know it is a great place to keep learning. But I do really appreciate your help and others it really does help share knowledge that has grown over time to those like myself just starting out 

[areich]

I think in this case the value is affected much more by the modern repair and the very bad scratches than by the original test cut. Collectors looking for perfect examples will choose an owl without a test cut but they are perfectly normal and very common on owls.

[superflex]

Thanks areich, that's what i was thinking when i purchased it from a common sense perspective. I brought it close to $100, looking around prior to purchase for similar coins it seemed like a good value deal at that price point. Hopefully one day i can trade up to a perfect looking owl, they are not cheap ! 

[daverino]

 I saw that coin for sale and was myself tempted. But what causes that peculiar type of damage to the obverse?

   It is quite similar to that I used to find among 'uncleaned' coins in which one face of the coin is disfigured and yet the rest of the coin is in very good condition - No, I never found any Owls in my uncleaned sets. What has most likely happened is that another coin has fused to the other while in the ground. The coin or object made of a less noble metal (iron in this case) has eroded away while acting as what is called a "sacrificial anode" preserving the metal quality of the Owl but leaving a badly damaged spot on the face of Athena where they were once fused together. Electrons travel from the iron object to the silver as in a battery. The silver thus remains in its reduced or metallic state while the iron object is oxidized to rust (iron oxide).

Here is an example from my collection. a Gordian of Odessos, where the reverse is near perfect but the obverse shows how another coin was fused to it in the soil. A $100 coin now for $15!!

I notice that coins like this appear usually with the obverse having the damage. Perhaps this is because this is the most value-sensitive side and therefore most likely to be up for sale at the bargain store.

Regards, Dave

[daverino]

One further thought may be in order, especially for the beginning coin collector. Damage like this substantially degrades the price of the coin but it also makes it affordable. The price of perfection in ancient (or modern) coins is very high. I think that it is possible to be satisfied with the less than perfect and still be able to appreciate the significance and beauty of these coins.

Regards, Dave