Dick Johnson submitted this excellent treatment on the subject of plating in numismatics. Thanks!
Paul G. Lajoie is cataloging his extensive collection of Statue of Liberty medals in preparation of publishing a catalog of these American idol collectibles. This week he encountered a Dieges & Clust medal that was marked: "xx gold." What was the meaning, he asked, of "xx gold?"
That is an invitation for me to talk about one of the core concepts of numismatics that is so unknown to coin collectors but is such vital information for medal collectors -- electroplating. Read carefully below; there is a quiz at the end of this discussion. To answer Paul's question first, here is what I sent him:
"xx gold" means gold plated in twice normal thickness. In effect the object is left in the plating tank a bit longer than for normal plating. The actual thickness is not that different -- it acquires the gold color early in plating. Perhaps more important is the composition of the base metal. It could be anything, but probably bronze. Brass is often used because it has a similar yellow color of gold. If the gold plating "bleeds" on such a medal showing the base metal, if brass it is not obvious.
Sounds like you are hard at work on your Statue of Liberty book. That's G R E A T!
Plating is the process of electroplating, the electrochemical process of depositing ions of a metal onto a base object. In the numismatic field it means a very thin layer of one metal is deposited on another metal already shaped by die striking or casting. This is done to improve the surface metal, its color or finish.
Electroplating is accomplished by electrolysis in plating tanks. The process uses electricity of low voltage direct current in a tank filled with a liquid electrolyte. Two electrodes are required, one of which is the item to be electroplated; it is the cathode. The other, the anode, is the source of metal to be deposited. It wears away like a bar of soap; it is sacrificial, as metal ions from the anode passes through the electrolyte, they are deposited on the cathode. Once the current is turned on, ions leave the anode, enter the electrolyte, and similar ions adhere to the cathode. The longer the item remains in the tank and the current kept on, the thicker will be the deposited layer of metal.
Generally, a precious metal is deposited on a less expensive metal, but virtually any metal can be deposited on any other metal. It might require an intermediate step, however. Gold, for example, does not bond to iron or aluminum. But it can be bonded to another metal first, say copper or nickel, then that item can be plated with gold.
Copper and copper alloys (such as bronze) are relateively inexpensive metals, and they actively bond with silver or gold, so they are widely used for shaping any item to be plated with a precious metal. You might be surprised to learn all those silver-plated tableware you have been using for years are actually struck in copper, then heavily plated with silver. These have been made in America since 1847. Thank you, Rogers Brothers.
The use of electroplating in the medallic field has a very wide use; medals are frequently plated. The most obvious reason is to create a rank of award. We all know the rank of medals range from bronze, the lowest, to silver, to gold the highest. But another surprise! All those Olympic Gold Medals are not pure gold. Even the most prestigious award medals in the Olympic Games, Olympic Gold, are actually struck in bronze and goldplated!
A typical medal to be plated is fully struck up, trimmed, and cleaned. It must be chemically clean, no grease or oil must be on its surface. (There are degreasing applications and chemicals on the market.) The medal must be free of surface debris and contaminates. Chemical cleaning creates an activated surface, one that is highly receptive to tarnish, thus the item to be plated must be inserted in the electroplating tanks as quickly as possible before this tarnish begins to form.
Medals are generally plated in a batch. So a number of medals are placed on a metal rack that is lowered into the electrolyte solution.
Usually the metal being plated can be observed in twenty minutes or so. A normal coating of a thousandth of an inch might take four hours. An extra heavy coating might require eight hours or more. (In the 19th century some items were marked -- like Paul's Dieges & Clust medal -- identifying the thickness of this plating: "xx gold" meant more than normal, "xxx gold" meant thickest plating of all.)
The electroplated metal is a thin coating. It will have the same properties on the surface as a solid medal of this metal. However, since it is a thin coating it can be worn off easily. Plated medals can be given a patina or relieved finish but care must be taken not to remove any of the thin coating. Plated medals, like all fine art medals, are almost always protected with a lacquer coating as a final step.
Plated medals wear at the high points first just like solid metal medals. Often a nose on a portrait as a high point will be first to display the under composition of the plated medal. When this occurs, it is called bleeding -- the under composition, the base metal, is exposed.
Since a silverplated item looks exactly like a solid silver item, the practice of hallmarking was created for anyone to distinguish between the two. This was necessary to indicate fineness. Plated items are not required to be so marked. Thus silver and other precious items made in the 20th century and later are required by law to indicate their fineness. This was first enacted in England in 1904. Tiffany & Co observed this and pressed for a similar law in the U.S.A., enacted 1906; thus American metalworkers call it the "Tiffany Law."
Electroplating requires an experienced operator. He must control a half dozen or more variables in the process all at once. These include such factors as voltage and current density, metal composition and cleanliness of the base surface metal, composition and purity of the anode, composition of the electrolyte solution, its pH, temperature, agitation, and other chemical factors, plus other factors. Impurities in any of these affects a desired deposition. They create electroplating anomalies (a rare form of "mint errors.")
There are so many other components of electroplating that apply to numismatic items. Perhaps they should be discussed at a later time. These include partial plating -- how to plate only a portion of a medallic surface; reverse plating -- salvaging the gold from a goldplated item; bright plating -- a surface with high reflectiveness; flash plating -- super thin coating; Sheffield plate -- plating before striking; anodizing for aluminum; and test cut -- how to determine the under composition of a plated item.
The word "plate" is also used in additional ways in the numismatic and medallic field: (1) the one side of a box medal; (2) the planchet for a side-by-side die at the Paris Mint for striking their Restrike Series; (3) large plates (like dinner plates that have been embellished with medallic items), and (4) a coin or medal illustrated on a plate in a printed catalog or book.
NOW FOR THE QUIZ: The Philadelphia Mint had electrolytic tanks from 1855 until recently. Yet, they never plated a coin or medal (to my knowledge, at least). What then, did they use these tanks for?
Answer next week.
Uh, goldfish? Anybody have a better answer? Interesting question!
Wayne Homren, Editor
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