Looking For Examples: Cast Pitting Vs Legitimate Pitting

It's a great issue you raise, jfk33. I've often struggled with this...that is, determining whether I'm seeing legit pitting/porosity on a coin versus evidence of casting. I've seen some coins that were condemned based on what I thought (and still think) may have been pitting.

I've heard some say that a basic difference to look for is whether the pits/holes are distributed evenly over the entire surface of a coin (supposedly an indication of casting), versus in a confined area (supposedly indicating it's legit corrosion). But I've seen plenty of fakes where the bubbles were confined, and legit coins - like this one - where the pits were evenly distributed...so that theory doesn't always hold true:



Note in the image above that the pits are more or less round too...so while perhaps pits may often be less circular than bubbles, there can be exceptions.

Obviously any assessment needs to be based on the whole picture: soft details? flow lines? evidence of filing? weight? notorious seller? are there any casting pearls (basically bubbles in relief), etc.

Bubbles in casting tend to be seen as "pearls" on the surface of the coin. The bubbles are created in the lost wax process when the 'investment' is mixed with water. A substance like Plaster of Paris is used to form the mold around a wax copy of the item. The process leaves no edge seams but requires the wax piece to be on a wax sprue which forms the channel through which the molten metal is later poured.
The bubbles in the plaster often cling to the surface of the object and are usually removed by a vibratory procedure. Most bubbles will let go and plaster uniformly cover the surface. It is almost impossible to remove all the micro bubbles and in areas of great detail they are most often found.
The tell tale sign of bubbles are tiny spheres usually in areas where they can cling to surrounding surface. The flat fields are usually clear of them.

Holes in the actual metal are most often caused by impurities in the metal. When the metal being cast is melted (usually in excess of 2000 degrees F) oxidation occurs and the surface need be cleared of 'slag' floating on the molten metal. When the metal is actually poured either centrifugal force (spinning it) or by placing the hot (wax free) investment on a vacuum pump will draw out any gases inside. Bubbles created in the actual pouring of the metal are usually large and irregular.
The 'bubbles' most likely to be seen on the surface are the 'pearls' which sit like tiny orbs.
Bubbles inside the metal are caused by impurities and tend to be concentrated around the sprue area. In complicated casting operations there may be more than one sprue. This gives better casting results but requires that more than one (now) metal sprue be cut and the surface area repaired.

Great topic . I have a 2003 maine quarter that has some pitting on it and on both sides and would like some info on how to post it . I looked over how to post pictures but it didnt work . please help thank you

Porosity caused by incorrect temperature of silver during casting resembles little pin holes everywhere. The same can be seen occasionally on genuine coins where the melting process to form the blank caused tiny air bubbles in the mix.

The tip off for me has usually been the lines left by cutting the rubbers off the pattern when lost wax casting. It leaves fine lines circumnavigating usually close to or on the edge of the coin.

A thorough forger can cure either issue, burnishing or running silver across the surface, cleaning up casting lines etc. Then there may be indications of that like rounded smooth edges, unnaturalness to the finish or flan cracks.

I am not an expert on identifying forgeries and can make errors like anyone else but I know to listen to my gut and never rely on a single indicator... its when everything is taken in its entirity you can form an opinion, the abscence of casting evidence after all doesn't prove something real.

If somebody wants to discuss the effects of electrolosis/interaction between coin and soil and how the metal migrates I should be interested to know exactly what evidence that leaves and whether is can be reproduced fruadulently.