Methods for Measuring Mint marks ?
krueger
Posts: 904 ✭✭✭✭
Does anyone have a method or know of a method (preferably easy) to measure mint marks.
using a measuring loupe is difficult and inaccurate. Maybe some software to measure off a photo??
Krueger
0
Comments
Do you want this for authentication purposes? How accurate do you want to be? I have used measuring loupes and found them to be accurate to .0005".... Cheers, RickO
It would be helpful to know WHY you wish to measure a mintmark. Without that - microscope eyepiece.
Otherwise, I'll bet their are folks here who know how to take an image of a coin's MMK with a scale of measurement in the frame. Then they can figure out at a certain magnification how the MMK measures. Most large/medium/small distinctions are naked eye determinations.
Question for you. The size of a mintmark can change with circulation. AFAIK, most authenticators go by its SHAPE. IMO, the only measurements really useful are the distances between other design elements.
Absolutely! The size, shape, and tilt of a mintmark in relation to position on the die is the first diagnostic for authenticity.
Pete
Mintmark measurement usefulness IMO has quite a few limitations, depending on why you would want to do so.
Given a singe mintmark punch being used, mintmark size will vary on coins due to: Mintmark die wear (slowly enlarge due to wear/flattening?), how hard the mintmark is punched into the die, whether multiple punches are used (doubling effects, etc.), the angle of the punch (uneven mintmark), etc.
Then you have changes due to die wear, die polishing, circulation of the coins, etc. But... in answer to OPS question, I myself am not aware of a simple software or camera setup that would be an easy or inexpensive way to do the measurements. I have used microscopes and software in an industry in which I worked to do some precise measurements, but these setups were more expensive than what I think the OPS post is wanting.
If the OP must do this, try:
Take all mintmark photos at the same subject-to-CCD magnification. This can be calibrated by photographing a typical mintmark, then substituting a high quality metal rule or a bar of accurately known length. Do not refocus - adjust the bar's distance from the lens until it is in focus just as was the mintmark.
Display the image on a monitor and compare the bar's original length with that on the screen. The ratio is your system magnification. Calculate the original mintmark height and width from this. (If all parts & distances remain identical, all your mintmark images will have the same magnification.)
The only repeatable mintmark measurements are at the highest plane of the letter. This is the minimum area of the mintmark punch's face and the only part that is independent of mintmark depth. (The punch letters are cut at an angle - the letter becomes wider as it is closer to the shank or base.)
A simple caliper?
Try measuring a mint mark with one and you may agree that using a simple caliper is an "impossible" and unreliable measurement.
Agreed. Calipers are useless. See the prior thread on the same/similar subject.