The Numismatic Bibliomania Society



The E-Sylum: Volume 22, Number 42, October 20, 2019, Article 13


Dick Johnson submitted this important but lengthy entry from his Encyclopedia of Coin and Medal Terminology. Thanks! It's a fascinating look behinds the scenes of a minting operation. Here's Part One. -Editor

Finish and Finishing. Any process that is performed to a medallic item (coins have no applied finish) after it is struck or cast; including antiquing, patinating, enameling, plating, fabricating, lacquering, edge stamping, mounting, other. At a plant that manufactures medals, other than the pressroom, the finishing department is the second largest department. Every struck piece, other than coin finish and proof surface, must pass through this finishing department for a number of processes to be applied to each piece, giving every medallic item its final color, appearance, protection and, often, its mounting.

The finishing department receives all the items in their final physical form, all the actions of the pressroom must be completed, all striking and trimming. The medals at this stage are called raw medals, they are completely struck up, all the design and all the lettering that is in the die or mold must be on every piece (some edgelettering or inscribing notwithstanding, these can be applied later). The finishing department must then perform their functions to transform those raw medals into works of medallic art with a most attractive surface that is to be protected for decades or centuries of their possible existence.

There is a very large metal finishing industry for processing most every manufactured metal object. However, the finishing procedures employed for medallic items have been adapted from this industry but occupy only a very small part of its technology, concentrating for the most part on finishes for bronze and silver objects.

Finishing department foreman. The foreman of the finishing department must be a craftsman with knowledge of metallurgy, chemistry, electrolysis and physics. He must be able to take a raw medal – fully struck up with every step of the pressroom completed – and transform that raw medal into a completed work of medallic art. He must have artistic knowledge as well and an aesthetic sense of what he is doing. He should be able to create any finish on a medal that he is called upon to produce (except, of course, coin finish or proof surface, neither of which receive any finishing).

The foreman must oversee every possible step of that medallic item through his department: its proper patina or other finish, its enameling (in proper color, if required), its electroplating (as goldplating or silverplating, if necessary), its fabrication (bringing several parts together if needed), its lacquering (for almost every piece) and complete the item with its suspension or mounting. Then pass this completed medallic masterpiece on to inspectors who will search for any misdeed of his department or imperfection of the piece before it is approved, packaged and prepared for shipment.

First step: abrasive blasting. The usual first step for most every item in the finishing department is to abrasive blast the raw medal. This creates a roughness on the surface, microscopic craters, called cups, cover the entire surface. They are called cups because they can hold liquid. A number of the steps to follow will use liquid to color, to antique, or patina the metal surface.

The abrasive can be any of several kinds, sand, pumice or glass beads. Originally a fine grain sand was used and the process was called sandblasting. Modern technology is able to create glass beads in an even finer grit, so this abrasive has replaced sand. Medals are laid flat on a large rotating tray within an enclosed hood. Nozzles pelt the exposed surface of the medals with the abrasive under pressure.

Impacting the medal's surface with thousands of microscopic cups per square inch, the abrasive breaks up the smooth surface created by the die in the pressroom. The tiny grains fall off the medal and pass through holes in the rotating tray to a receptacle below where the abrasive is recycled to be used again by the nozzles above. All effort is made to contain the abrasive within the confines of the machine as it is used over again.

The color of the medals change most dramatically in this step. Raw medals are usually bright: bronze is usually bright red like a shinny penny, silver a light reflective gray. The abrasive is usually matte gray, and the surface of the medals take on this matte gray appearance. The pelting affects only the exposed side only, so the medals have to be turned over by hand and allowed to rotate under the nozzles for the opposite side to be abrasive blasted as well. It is not necessary to sandblast the edge, even on a thick medal.

The treated medals are picked out by hand, the excess abrasive is shaken off, then placed in wire baskets, perhaps a dozen at a time. The medals are placed vertically in a long handle wire basket in such a way that both sides are exposed. The medals are prepared now for either an antique finish (by oxidation and relieving), or a patina finish. The surface is now suitable for treating with a liquid (in the microscopic cups).

Oxidation (actually a sulphatization). The wire basket containing the abrasive-blasted medals are then immersed in a bucket containing the darkening chemical (as ammonium sulfide) for the next step of antiquing. The wire basket is rotated by hand holding the handle, swishing it around submerged in the liquid so it comes in contact with as much of every medal's surface as possible.

Time is quite critical. The chemical acts quickly. The medals turn black almost immediately. The sulfur from the ammonium sulfide combines with the surface molecules of the bronze or silver to form copper sulfide or silver sulfide. The metal reacts instantly with the sulfide, the process of sulphatization (unfortunately it is called oxidation, which implies oxygen, but the reactive ingredient is the sulphur, no oxygen is required). This chemical action occurs in from five to ten seconds.

The medals are again changed in color (as well as their surface changed chemically). From gray abrasive blasted, they are now black. The operator can control the blackening somewhat. In the first few seconds bronze turns dark brown, then black (silver turns black immediately). The longer the medals are left in the solution, the darker (blacker) they become, reaching a maximum blackness in the ten seconds.

The wire basket containing the medals is removed from the bucket containing the darkener and immediately immersed in water. This stops the chemical action. Then fresh water is run over the medals to wash away any remaining darkening chemical, and any residual abrasive. The wet medals are removed from the wire basket, placed in a tote box and moved to the relieving station.

Book lovers should be word lovers as well.

Looking for the meaning of a numismatic word, or the description of a term?  Try the Newman Numismatic Portal's Numismatic Dictionary at:

Or if you would like a printed copy of the complete Encyclopedia, it is available. There are 1,854 terms, on 678 pages, in The Encyclopedia of Coin and Medal Technology. Even running two a week would require more than 19 years to publish them all. If you would like an advance draft of this vital reference work it may be obtained from the author for your check of $50 sent postpaid. Dick Johnson, 139 Thompson Drive, Torrington, CT 06790.

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