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Most ancient coins were hammer struck on hand-made or cast flans struck between a hand-held upper die and mounted lower die. Many things can, and often did, go wrong in such a process and perfectly struck ancient coins are rare. Since minor striking imperfections are to be expected, unless they significantly detract from the the eye appeal (and therefore the value) they need not be discussed other than for the highest grades (gXF and better). Unfortunately, many striking imperfections significantly reduce eye appeal and need to be described in enough detail to give an accurate idea of what the coin will look like. Failure to mention significant striking defects is justification for returning a coin to a seller.
WEAK IMAGE
Due to low die pressure
Most ancient coins were hand struck, the strength of the image on a coin is significantly affected by how hard the hammer hit the die. It is not unusual to see ancient coins struck with a weak hammer blow, resulting in only part of the image being transferred from the dies to the coin.
On this Odessa tetradrachm, the center of the coin is very flat with almost no detail across Zeus' hips. Yet the rest of the coin is fairly strong (note the strong detail on Zeus' head). This is an example of not enough die pressure to push metal into the highest point of the design, and the correct description of this reverse is VF with a weak area.
On coins struck with flat dies, such as that illustrated above, the weakness will be most notable on the highest point of the coin, but can be present to a lesser degree over the whole surface, giving an appearance similar to a worn coin. On coins struck with convex dies, weak die pressure results in the strongest impression in the center of the coin, becoming progressively weaker towards the edges (which is why many Roman sestertii have strong portraits and weak inscriptions).
WEAK IMAGE
Due to Die Wear
This is also discussed briefly under grading, but it needs to be dealt with here in a little more detail. In normal circulation a coin normally wears evenly on both sides, yet one commonly sees ancient coins that appear to have very little wear on one side, and are heavily worn on the other. In most cases, this results from the "worn" side having been struck with a worn die and that side of the coin appeared worn the moment it was struck.
This ancient Indian coin illustrates this fairly well with an obverse grading VF, but a barely recognizable reverse. We can see enough of the design to know it is not a centering problem, and the strong obverse strike eliminates weak die pressure. The strong image around the edges of the reverse show the actual amount of wear to be about the same as on the obverse, which leaves weakness due to a worn die as the most likely cause. The result is a coin with greatly diminished eye appeal which technically grades VF/Fair and is worth only a fraction of what a VF example would be.
WEAKNESS DUE TO TILTED DIE
A perfect impression is only possible if the surfaces of the dies are roughly parallel to each other at the time of striking. The lower (obverse) die is fixed but the upper (reverse) die is hand held and it is easy for it to become slightly tilted at the moment of striking. This will result in a stronger impression on the side where the two dies are closest together, and a weaker impression on the side where they are furthest apart. Sometimes the weakness will become gradually stronger as you move across the design, and often both sides of the coin will show a similar weak area in the position directly opposite each other.
Click on image for enlargement
Note how in the obverse of this coin the leaves on the left side are very strongly struck with well defined borders of dots but on the left side the borders are barely defined at all. This specimen has a die rotation of about 340 degrees, so I have rotated the reverse on the image. You can see the two sides on the same orientation, and you can see that the inscription on the reverse is weak in exactly the same position as the weak leaves on the obverse.
The description of this specimen would be gVF with a weak edge, although most Jewish revolt denarii will show this type of strike and this particular specimen actually has a better than average strike for the issue.
WEAKNESS DUE TO THIN FLAN AREAS
When there is a thin spot in a coin's flan the dies will not make proper contact with the flan at that point, resulting in an area that received a very weak impression, and sometimes none at all. Normally the weakness will be present on both sides of the coin, and while on a two dimensional image it looks similar to weakness due to low die pressure (weak strike), when actually holding the coin you can clearly see and feel that the coin is thin at the weak point. This problem is rare on gold coins, less common on silver, and fairly common on some larger bronze coins (especially large Greek bronzes).
Notice the missing details in the center of the obverse and reverse, but strong and sharp details around the edges, as is typical of coins struck with a thin area in the center of the flan. There is little wear on this coin (note how sharp the details of the drapery are) and technically grades XF for wear, but the weak area only allows the same amount of detail to show as one would expect on a typical Fine, and the eye-appeal is certainly much lower than for a typical XF. One could properly describe this an an XF with a very weak central area, and it should sell for a price similar to a normal gF to VF specimen.
WEAK EDGES
Above we have have already discussed how low die pressure, combined with a convex die, will result in some coins having a strong central design but with very weak inscriptions at the edges. A very similar impression will result if the flan is slightly convex and the die pressure is not high enough to flatten it out.
DOUBLE STRIKES
Many ancient coins had to be struck more than once to get a proper transfer of an image to the flan. Generally the larger the coin and the higher the relief, the more strikes would have been needed, but smaller coins are effected by this as well. Usually the multiple strikes occur exactly on top of each other and are not apparent, but occasionally one or both of the dies shifted slightly resulting in a clearly visible doubling of the image. Because the second strike normally obliterates most of the first strike, the doubling will usually only be visible on areas of the coin where the second strike does not overlay the first. Occasionally doubling can be very dramatic with significant rotations as well as off-sets.
Click on image for enlargement
Note how on this Kios hemidrachm the obverse shows no sign of having been double struck, but the ghosting of the prow on the right side of the reverse shows a double strike with a significant off-set between the two strikes. At first glance this appears to be only a minor, not terribly noticeable detraction from the coins eye-appeal, except that if you are familiar with these coins you may notice that the doubling has significantly reduced the clarity of the inscription below the prow.
Doubling only visible under magnification is fairly normal and need not be described, but doubling clearly visible to the naked eye is significant, affecting the coin's eye-appeal and value, and should be described.
Generally, poor strikes significantly reduce a coin's eye appeal and with it the value, but one has to be careful. There are many ancient coins that are only known from poorly struck specimens and if you wait for a really nice one, you may never find one. There are even some rare examples of early Greek coins that were struck on one side, then turned over and struck on the other side, with the result that the side struck first is always in part obliterated. Again, this comes down to experience and research and knowing what to expect from a given type.
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