Post your best "Authenticity Challenged" Coin; I'll start with my 1872-S hd

Likewise, I have my doubts as to this being struck from CNC-milled dies.

I know that machinists would be in my ear 24 hours a day about tool and program changes to execute such fine detail and relief work on the dies. I think one reason so many modern coins are much less sophisticated in design than the Seated Liberty design is to limit the number of depths of cutting path and tool changes.

Moreover, scanning the deepest, narrowest recesses in the Seated Liberty design is another challenge not easily overcome, even before attempting to machine the dies.

I'm not saying it cannot be done, however, someone with the level of sophistication required to pull this off would probably not overlook the need to use a genuine rare coin to do so, rather than bringing together dies made from different years that could more easily be spotted.

 

Have you determined with certainty how the dies used to strike these coins were manufactured Jack? If they were indeed milled from scans of genuine coins we are in a heap of trouble going forward.

 

One way to possibly tell the difference would be difficult, but irrefutable.

Both scanning and machining equipment can make errors in both directions. In manufacturing vernacular, tolerances on size and location are bilateral, and can occur in both the positive and negative directions.

Small features, such as the diameter of a dot or the thickness of a line for two examples, may grow when transfer dies are employed, but they cannot get smaller. This is not true of digitally replicated features.

As good as makers of 3D manufacturing equipment try to be, the output from the scan has a +/- tolerance on it, as does the positioning of the cutting tool on the milling machine. That means the tool may be out of position as much as the tolerance on those 2 pieces of equipment allow.

For example, if the scanner output has an accuracy tolerance of +/-.001" and the milling center has an accuracy tolerance of +/-.002", theoretically, the cut surface could be as much as .003" out of position. That means opposing surfaces (the diameter of a dot or the thickness of a line) could be out as much as .006". Said differently, the dot / line could be as much as .006" smaller / thinner, or as much as .006" larger / thicker than the scanned feature.

That's not to say the surfaces would be out of position at all. The equipment manufacturer just allows for that much error in the design and manufacture of their equipment. What's daunting is when one is made to the high side (MMC for GD&T geeks), and the other to the low side (LMC), the tolerances are offsetting, and the end result may in fact be nearly perfect.

Still, if measured and found to be smaller than the real thing, it rules out transfer dies and points to digital replication.

It's probably premature to go down this path today, but it may become necessary in the future.

 

You're correct, but the same positioning tolerances apply to that process as well. In addition, because of additional errors inherent in laser etching (tolerances on power supplied, travel speed (or dwell time), and focal distance from laser to target of ablation), the potential resultant errors in position or feature rendering should be even greater than for machining.

I've no experience looking for this on coins, and thus haven't proven it to myself, but the amount of energy required to remove material is a function of how much the local mass in target areas varies (local mass affects how fast heat sinks away from the target). The more mass, the slower the cutting speed should be.

The proximity of the laser to the detail being etched (the aforementioned focal distance) also dictates adjustments to the energy input to the process.

Since the depth of cut varies considerably on a coin's surface, it stands to reason that the quality of etching will vary somewhat in different areas. This may be a good way of determining if a coin has been replicated with a laser.

 

Thanks for that.

While I'm no Canadian coin afficianado, I am interested in the variation in quality rendered by laser etching based on different conditions presented by the design.

Can you direct me to more images?

 

The companies you mention manufacture medical lasers for opthalmic and cosmetic surgery on non-metallic targets. With their high precision controls, and pulsed output, they are well-suited to their target markets, but nowhere near powerful enough to precisely etch the materials we are discussing.

Even if they offered higher powered models, the challenges of managing the moving targets of variable focal distance and variable local mass remain.

 

All metalworking processes have made significant strides out of necessity in order for the USA to remain competitive. Despite that, the equipment still is not perfect, and never will be.

The quality of the machinery may have improved enough to fool us, but every process has some "weakness" that makes a different process preferable for some workpieces. Those weaknesses are likely the areas we should be targeting to identify the "tells" you seek.

One weakness I can think of regarding laser ablation is that it probably concentrates too much energy for too long in sharp interior corners of a die where a reversal in direction is required to avoid a new start of the laser. That may result in some flowing of overheated material in such sharp corners. That sharp interior corner in the die might be found at one of the 3 acute exterior corners forming the arrowheads either side if the date, but I'd think a sharply struck nearly mint state example may be necessary to do that.

Getting ready for Baltimore, so I'll have to think more about this another time. If you'll be there, please stop by. I'll be at table 556.

- Mike

 

Sorry you can’t go Jack. I’m pretty darned excited . . . I’ve sat out since Feb 2020, and this will be my first time back.

Thanks for the offer. Unfortunately, I think I’d need a suspected “daughter” coin to compare with your “mother” coin in order to determine if my theory holds any water, so until then, I’ll have to pass. Do you know of anyone who has one of the condemned “offspring”?