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REFERENCE GUIDES: Grading & Quality Of Ancient Coins


Damage covers a lot of ground and there is no way to discuss it in depth here. It is simply important to note that any form of damage can significantly reduce the value of a coin. This is also true of damage that has been repaired in some way. Because many forms of damage, and especially repaired damage, are not clearly visible on many images, it should always be discussed even when an image is provided.



Many things can happen to an ancient coin that has lain in the ground for up to 2500 years, but by far the most common is corrosion of the surfaces due to chemicals in the ground waters. Gold coins are very seldom affected by any type of corrosion, and while not too common, some silver coins suffer from corrosion, but surface corrosion is very common on bronze coins (to the extent that a high percentage of bronze coins are found corroded to the point they are almost un-identifiable).

corroded bronze
Click on image for enlargement

This Alexander the Great bronze suffers from two problems. The first is the light brown encrustations which are not a major problem because they can easily be removed without damage to the coin. The more serious problem is the light green spots which are actually fairly deep pits in the surface where the patination and underlying metal have corroded away. There is nothing that can be done about them because the metal is gone (anything done to fill them in and hide them, and sell it as a nice coin, would amount to fraud). The pinpoints of corrosion on this coin are minor, but they seriously detract from the eye-appeal and the value. You can image what this coin would look like if it were corroded over much of its surface (at which point it would become almost worthless).

With this type of corrosion on a bronze coin (especially when you see that powdery light green color), there is a high danger that the coin suffers from bronze disease, and that chloride reaction inside the coin will cause the corrosion process to continue and eventually destroy the coin (if you own a coin with these types of spots, and the spots get bigger or a soft green powder develops in them, the coin will have to be treated to stabilize it).

On silver coins corrosion can be a problem, but a much bigger problem is crystallization exposed on the surface. The majority of ancient silver coins have internal crystallization, as it tends to happen naturally to silver over long periods of time, but normally one see's no evidence of it on the surface. This is because the outer skin of a coin becomes highly stressed during striking, and such stressed metal normally remains non-crystallized. When this outer skin is removed, or if the conditions of burial force even the skin to crystallize, the coins surfaces become slightly rough.

Click on image for enlargement

This Maroneia hemi-drachm is an interesting example because it has light crystallization over about half of the surface, with the other half a normal smooth surface. The crystallization on it is minor and on the normal sized image not noticeable, although with the coin in hand one does notice the slight roughness. If you click on the image for the enlargement you can see more clearly how the crystallization is visible on only the left side of the coin. Crystallization like this is a double edged sword. When light like this it does detract from the eye-appeal, but only slightly. On the other hand, it is one of the most difficult things for a forger to duplicate and thus is a good sign of authenticity.

The real problem occurs when a heavily crystallized silver coin suffers significant surface corrosion, as with the Philip III tetradrachm below.

Click on image for enlargement

While grading VF with average centering, corrosion has exposed large areas of the internal crystallization, resulting in a very ugly coin, worth only a fraction of what a naturally smooth specimen would be worth.

It is important to realize most ancient silver coins are internally crystallized, and cleaning them with any method that removes surface metal may expose the crystallization making the coin rather ugly. It is also important to note that crystallization makes coins slightly fragile and some ancient silver coins could break if dropped. Since you normally cannot tell the degree of crystallization by looking at the surfaces, all ancient coins should be handled carefully.



Man-made damage takes many forms including things that happened in both ancient and modern times. During ancient times many coins were test-cut to confirm they were solid silver (rather than plated base-metal counterfeits) which significantly reduces the value. Many coins show light knocks and abrasions resulting from normal circulation, which must be considered in grading and valuing, for they are detractions even if they occurred in ancient times. Still others received counter-stamps and bankers stamps which are technically damage but sometimes collectable in their own right and occasionally may even increase a coins value.

ptolomy iii 4 dr.

This Ptolemy I tetradrachm has multiple banker or merchant stamps applied to both sides in ancient times. While the stamps significantly reduce the coin's value, they are of great interest to certain collectors who study such marks and are very happy to find such coins available at the right price.

Athens 4 dr. grafitti
Click on image for enlargement

Another type of ancient damage is grafitti, where someone in ancient times engraved a light design into the coin. Normally this will take the form of one or more letters (probably the initials of the coins owner), but it could be almost anything. Unlike countermarks, which were officially applied and thus of interest to many collectors, there is little (or no) collector interest in grafitti on ancient coins and it is almost always a detraction that significantly affects the value. One of the problems with graffiti is that it is normally very lightly engraved and often not clear on images, so dealers should always make note of it in their written descriptions.

On the Athens tetradrachm illustrated above it is fairly easy to overlook the two Greek letters Alpha and Lamda lightly engraved into the field just to the right of the Owl, but if you click on the image you will get a much better view of them. This type of grafitti does reduce a coin's value, but the amount of a reduction is a function of how noticeable the grafitti is and the coin's grade. Light grafitti on a choice XF coin will dramatically reduce the value, but have little or no impact on the value of a coin grading only VG.



Of a more serious nature is the damage inflicted in modern times. Some is accidental, such as a mark from a spade hitting a coin being dug up. Far more common is damage from improper cleaning or handling (in part discussed under patinations), which can leave a coin with rough and pitted surfaces, or scratches and scrapes from cleaning with sharp tools. A potentially nice ancient coin can be greatly reduced in value in this way, and in a worst case it can be reduced to an almost worthless lump of metal.

One of the most insidious types of damage is tooling, which is the engraving of designs onto a coin that were not present when the coin was found. It can be re-engraving of designs missing due to wear or bad strike, or the creation of new designs that would never have been present on the type. This is very different from cleaning to expose designs present but covered by dirt and encrustations. Tooled coins are only one step away from being fakes and while the eye-appeal of a coin might be increased, such coins have little value.

tooled AS
Click on image for enlargement

At a glance this looks like a VF Agrippa As. There is an almost complete rostral crown, and most of the hair details are present. However, if you click on the image for an enlargement of those details, you will see that all of the crown and almost all of the hair details are re-engraved (tooled) in modern times. The coin probably only graded VG to Fine before tooling and today is worth very little.

Another common form of damage is found on coins once mounted in jewelry. Pin mounts or loops soldered to the edge or surface will always leave damage when removed, and claw type mounts will normally leave light damage where the claws clamped the edges. Even coins carefully bezel mounted, so that the bezel can be removed without harm to the coin, will suffer to a degree because coins worn as jewelry have different wear patterns than those in normally circulation, and they can look very unnatural at first glance (some such genuine coins can look so unnatural that they can be mistaken for fakes).



Hadrian denarius

This Hadrian denarius at a glance looks fairly nice on the image, and when I purchased it, it looked fairly nice in the hand. There is a minor area of corrosion just in front of the chin, but the high grade and nice style of the portrait made up for that and the coin was still very collectable at a slightly reduced price. However, when I got it home and was cataloging it, I noticed something that I missed earlier. If you look at the image closely you will see that there is a slight color shift on the back half of the neck, which is caused by light reflecting from the surface very slightly in that area. When I put the coin under a microscope to see what was causing it I saw the following :

neck repair

Note how the back of the neck has been somewhat flattened, with scrape marks. This is a clear indication the coin has been smoothed there, probably to repair a gouge or heavy scratches. The degree to which this effects the value is a little problematical. Assuming a collector is willing to accept this coin in his collection (and many would see it is still a very attractive coin in the hand, and you need a microscope to see the repair), the coin is certainly worth less than if it were problem free, but more than it would have been if it still showed a gouge or scratches. I actually paid a fair amount for this specimen as it has a really nice Neptune reverse, but will now have to sell it at a loss.


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