Edge Ribbon Seam. A Doubt

These Cap and Rays will be a little more difficult unless they are analyzed in a large sample size. I suspect the following:

1. The number of base core alloys will be less as you suggest than compared to the Bust Types: brass, bronze, copper and German silver. So far after a dozen examples I have recorded only low zinc (Zn:2-8%) brass and a high copper alloy (Cu:98%+). No bronze or German silver (Cu/Zn/Ni) or any TIN in any of these examples for that matter. Again a VERY small sample size.
2. You probably have a better idea if the Patio process was used on the silver to electroplate these pieces. Is the Hg found here over 1% the result of this process or something else like this Ag stripping operation. These super high levels suggest something else since the Hg was found in some copper looking areas and not on the Ag spots of the coin!
3. If you look in MEX literature a lot of the non-silver tokens and coins are classed as bronze yet I am NOT finding this alloy when looking into this arena. Consider - how much will low zinc brass look like bronze? It's the high zinc (>10% Zn) that really imparts the yellow color to the brass alloy - of course from previous investigations as in the Canadian Blacksmiths which I detail in my new book. If not yellow it must be bronze to the collector - WRONG! It could be low zinc brass - more likely? Still investigating. I am sure SOME MEX issues are strictly bronze as I investigate more issues.
4. Unless you are dealing with AU or UNC examples it may be difficult to achieve this near 99.9% Ag surface readings on these electroplated Cap and Rays. Also how much is due to silver enrichment ... however Ag enrichment as we discussed with the Bust CC8R's normally go up a couple of percentage points to the 92-96% range as we have seen and NEVER peg at 99%. Something to consider/agree moving forward.
5. With electroplated silver being a thin film I wonder what metal was introduced to bring the weight to NEAR regal on some issues. Lead? Not sure if you have assayed Au or UNC CC8R C&Rs for THIS answer - yet.

Just some thoughts off the top of my head ...

JPL

I will start with the schematics of both conditions first and follow with photos.

First of all I have examined several examples under high magnification (binocular) and there is a difference. The line seen on Sheffield coins with edge ribbons is a flat seam line. The dentils run through the seam at the same level. The same is not the case with the "apparent seam" that austrokiwi refers to. He is seeing a groove that runs through the dentils and is caused by a lack of metal to in-fill the die. The outer side of the groove (radially) is typically formed at a steeper angle than the inner side of the groove which is a lower angle.

After reviewing the pressures involved - there is a simple reason based on physics for the two different grooves.

First the austro-kiwi groove.

This appears on numerous screw press struck coins that are edged before the strike. It is often stronger on one side than the other and the depth of the groove is dependent on the way the edge design was centered. (More to follow on that point from the photos).

We start with a blank cut from the rolled silver.



This blank is upset (raised edge created) during the edging step. Note the edge detail is recessed into the face of the edge die and the slot is thicker than the coin.



What this results in is a thickened edge which spreads to the width of the groove in the edge die.



The edged blank - now called a planchet goes into the screw press. The dies mounted in the screw press are larger than the coin diameter and the dentils are cut into the die FLAT. They are not cut into the die on an angle.



After the strike the raised rim has filled the outer part of the dentils and the flow from the field has filled the inner part of the dentils. When the upset is too high which occurs when the edge is applied eccentrically a groove is created between the two fills.



That is what I see on the screw press coins of Austria and Switzerland. I have also seen it on some 8Rs from both colonial Spain and other mints employing screw presses.

Next I will explain the ribbon edge.

Sheffield Plate is a welded composite section of metal that after it is welded acts as a unit. It bends and deforms as if it was homogeneous.

It looks like this. But remember that the outer silver layers are only 2 - 7 thousandths of an inch thick more like a thick foil layer. The edge ribbon is solid silver about the same thickness.



When the silver ribbon is applied to the raw Sheffield blank it extends slightly (1/8th inch or so) over the edge. It is also bent inward toward the faces of the coin - how far no one knows.



In the cases I have reviewed, I tend to believe the edge is folded over onto the face of the coin because there are no large folds present.



The final step is the strike. Remember two facts:
1) The silver layers are very thin.
2) Silver and copper bend, fold and are distorted in identically the same way by pressure.

The result is a cross section that must (based on the principles of physics) look about like this.



This is a schematic representation of what I see when looking at each type of coin under a binocular microscope.

The edge ribbon is seen with complete dentils where both inner and outer portions meet at a POINT. The only space observed comes with minor (0.001) chipping along the line.

The edge described by Austrokiwi is a far deeper groove that was created as a result of the upsetting of the rim in a normal edger.

I have to leave this until I transfer the photos because it is after midnight here.