Reading a coin's surface
The things that took me longest to work out, written down. No account needed and nothing to buy to read them.
Raised or incuse: the question everything else hangs on
Almost every argument about a line on a coin is really this question. A raised line was put there by the die when the coin was struck, and is part of the coin as it was made. An incuse line was cut into the coin afterwards, and is damage. One can add substantial value. The other subtracts it.
They can look identical straight-on. The way to tell them apart is not magnification, it is light direction. Put a single light low and to one side. A raised line throws its shadow away from the light. An incuse line fills with shadow on the side facing it. Move the light to the other side and the shadow flips to the other side of the line. That flip is the answer, and it takes two seconds once you know to look for it.
This is why a fixed ring light around the lens is the worst possible lighting for coin examination. It lights from every direction at once, so nothing casts a directional shadow and the one diagnostic that settles the question is destroyed.
The four kinds of line, and what each is worth
Die crack — raised, collectable
The die itself cracked, and metal flowed into the gap, so the coin carries a raised ridge. It wanders irregularly, often starts at the rim or at a letter, and grows through the die's life. That growth is useful: it lets coins from one die be put in order of when they were struck.
Die gouge — raised, collectable
Something scored the die, and the coin shows a raised ridge where the groove was. Usually straighter and heavier than a crack.
Die polish — raised, normal
Fine raised lines from the die being polished. Typically many, fine, and running mostly in one direction across the fields. Entirely normal and not damage, though it is regularly mistaken for cleaning hairlines by people who have just learnt to worry about cleaning.
Scratches and cleaning hairlines — incuse, damage
Cut into the coin after it left the mint. Cleaning hairlines are the giveaway of a wiped coin: many fine parallel lines, usually running in one direction across the high points, where a cloth travelled. Distinguishing them from die polish is the single most valuable skill on this page. Polish is raised and lives in the fields. Hairlines are incuse and cross the devices.
Doubling, and why it is so often wrong
Not all doubling is worth anything, and the difference is where it happened.
Hub doubling happened when the die was made, so every coin from that die carries it identically. The secondary image has rounded, fully formed detail, and notching at the corners of letters. This is the kind worth money.
Machine doubling happened at the moment of striking, when the die shifted. It leaves a flat, shiny shelf rather than rounded detail, it looks smeared, and it is worth nothing. It is far more common than the other kind, which is why most excited posts about a doubled die are not one.
Die deterioration is a worn die smearing metal, and is also worth nothing.
The practical test is to look at the corners of a letter under raking light. Rounded and notched, with the secondary image having real relief, points to hub doubling. A flat shiny ledge points to machine doubling. If the whole coin looks doubled in the same direction with no notching anywhere, be suspicious.
Why lighting is most of coin photography
Copper and silver are mirrors with a texture. What a camera records is almost entirely determined by what the surface is reflecting, which means you are not photographing the coin so much as photographing your lighting as reshaped by the coin.
Three changes that improve almost anyone's photographs immediately:
- Move the light off-axis. Low and to one side, not straight down.
- Diffuse it. A sheet of printer paper between lamp and coin turns hard glare into readable lustre. This costs nothing and is frequently the biggest single improvement available.
- Darken the surround. Your ceiling and your shirt are both currently visible in the fields of your coins.
Lustre, and why it photographs badly
Lustre is not shininess. It is a field of microscopic flow lines left as metal moved outward under the die, and it is what produces the rotating "cartwheel" effect when a coin is tilted under a light. It is also the first thing to go with wear, which is why it matters so much to grading.
It is difficult to photograph because it only appears at particular angles. A flat, diffuse light shows almost none of it on a coin that has plenty. This is worth remembering before concluding from a photograph that a coin is dull, and before trusting any software figure for lustre across two coins shot under different lights.
Wear starts at the high points
Circulation flattens whatever stands proudest first. On a Lincoln cent that is the cheekbone, the jaw and the hair above the ear. Knowing the high points of a series tells you where to look to place a grade, and it is why a grade based on the overall impression of a coin is usually optimistic.
Inside the program
NumismaticsU ships with NumismaLab and goes further than this page: structured lessons, a grading reference, several hundred coins worth knowing, confirmed VAM listings with their die markers described, and a hardware guide. It is reading rather than an instrument, so it opens in its own window.
None of it is reproduced from the grading services or the variety sites. It is written for the program.
