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The E-Sylum: Volume 23, Number 4, January 26, 2020, Article 16

VOCABULARY TERM: PATINA, PART 1

Dick Johnson submitted this entry from his Encyclopedia of Coin and Medal Terminology. It's the first of two parts on an important numismatic topic - patina. Thanks. -Editor

Patina. Surface coloration; any of a variety of finishes that are applied to a metal surface to give it color and protective finish. The term derives from the green finish – incrusted patina – of bronze buried underground. This process, known since ancient times, is a very slow chemical reaction; incrusted patina forms from the copper in the bronze in contact with sulfur in the soil or surroundings to form green copper sulfate. Buried bronze coins and statues give the best evidence of incrusted patina.

Fortunately the two metals most suitable for applying artistic patinas as a modern process are also excellent in casting and striking – copper and silver. Each metal composition, however, will have its own patina requirements. When artificially applied, silver and silver alloys have a narrow range of color patinas, grays and blacks. Copper and bronze have a very wide range of color patinas, predominantly browns and greens.

With extreme skill, however, a patina finisher (a patinaeur) can color bronze any color of the rainbow as well as white and black. Also of importance, if a patina color is unsatisfactory, the piece can be repatinated –the old patina can be removed and/or a new patina can be applied over it.

Patinas add permanent color to a metal surface, give it protection and enhance the beauty of the design. It does not add texture to the surface, nor does it create relief. Patina is not paint, it is not a coating, it is not transparent. Instead a patina will color the top layer of molecules of a metal surface by changing their chemical properties. Thus it is permanent unless the surface is treated with chemicals again.

Patinas for medallic items are the same as those applied to statues. However, since medallic items are comparatively small, their processing can be done on a production line bases and often more varied. Statues are usually one of a kind with larger surface area, and for repatinating must be done on location where the sculpture cannot be removed to a workshop. Medals are processed for patina work in the finishing department of a medal plant and done by the batch process under far more controlled conditions.

Techniques of patina applications. Patinas are not simple immersions of medals in some liquid that magically transforms a raw medal into a colored medallic item, and to dip the medal in another liquid to get a different color (like Easter egg coloring). Instead a patina finish is a combination of the coloring agent – a chemical – and technique of its application plus the skill of the finisher.

Typical patina applications are wet wheel, torch finish, brush finish, immersion finish, appressed finish and vapor finish. Brush finishes have a wide range of applications with the use of different brushes: stipple brush, wire brush, bristle brush, scratch brush and bristle wheel. The chemical can be applied at room temperature, hot, boiling or applied with a blow torch. Application methods differ widely adding to the many variables of these techniques. Detailed descriptions are given in the entries on these patina applications.

Variables affecting patinas. The alloy composition of the metal object to be finished is the foremost variable, followed by the chemical(s) used to effect the color desired; temperatures and time are also major variables in patina work. What metals make up the object's alloy? The tiniest amount of lead or phosphorous in the bronze alloy, for example, will greatly alter the outcome of the applied patina. The pH factor (degree of acidity) of the chemicals is always important in acid patinas. How fresh are the chemicals? Are they full strength, or have they been diluted?

Some patinas require the chemical to be applied to a hot surface, or the chemical itself to be boiling. Is the temperature above a minimum, or does it require a precise degree? How long should the chemical be applied? Should it be applied with a cloth, a sponge, or a brush? Should it be brushed on or stippled? With a bristle brush or wire brush. Does it have to be buffed? With a wet wheel or a crimp-wire wheel? Or does it require the item to be immersed? For a few seconds? Or for several days? Is a single color satisfactory? Or are two or more colors required? How strong must the undercolor be? Does the overcolor have to be translucent?

While extensive experience is required for applying a patina, knowledge of the numerous variables is also required and how to correct an unsatisfactory color. Fortunately most objects can be repatinated until the correct control of variables can be mastered and the desired color can be achieved. A particularly attractive patina process, perhaps developed in secret, is known as a proprietary patina if the developer wishes it to remain secret. But because of the large number of patinas published in Hughes & Rowe (Bibliography T11) it could probably be duplicated by others.

Color samples. An astute artist will want to exercise control over the patina of any medallic item he or she creates. The artist will often want to determine which patina his creations are to receive. Often the artist requests to be shown several proposed patinas – color samples – applied to the first cast or struck items so he can make a selection of the most appropriate patina finish.

Such a selected patina will become a patina standard toward which all produced later will be matched for color control. Even in a batch process, there are so many variables in patina work that no two specimens are exactly alike. Thus the patina standard is the color toward which all those produced are to be matched. (The degree of deviating from that color standard among the entire production run is a decision of the finishing department foreman.)

About 1910 the Gorham Company created a set of sample color panels in an attempt to standardize patina finishes (for small bronze statues). It also served the useful purpose of being able to show these panels to prospective customers to ascertain which patina finish to select that the firm could provide.

Types of patina. After extensive literature research and their own experiments, Hughes and Rowe lists 1,126 possible metal patinas. Of this number they recommended 344 formulas. Of this there are about four dozen that are widely employed by experienced patinaeurs in the art field (for statues and medals). An exact number cannot be stated because so much of what these craftsmen do is either proprietary (fine-tuned to their own needs) or their formulas and applications have not been published.

For numismatic purposes we can examine the patinas in two American art medal series and reveal these patinas and the process for their creation. These series are The Society of Medalists (129 medals) and the Great Religions of the World (18 medals). Here are the names and a typical bronze medal bearing that patina:

Bronze Patinas

Typical Medal Patina Color: SoM GRW

Blue (turquoise). . . . . . . . . . . – Catholic
Bronze, light.. . . . . . . . . . . . #1 Salvation Army
Bronze, light, glossy . . . . . . . . #101
Brown, dark.. . . . . . . . . . . . . #8 Presbyterian
Brown, dark with second color #41 Methodist
Brown, chocolate. . . . . . . . . . . #14 Lutheran
Brown, chocolate with green highlights #11
Brown-gray. . . . . . . . . . . . . . #84 Baha'i
Brown, light with green overcolor . – Islam
Brown, light with silver highlights . #87 Judaism
Brown, light with medium highlights . #83
Brown, mahogany.. . . . . . . . . . . #2
Brown, medium.. . . . . . . . . . . . #5
Brown, russet.. . . . . . . . . . . . #25 Buddhism
Brown with green highlights . . . . #3
Brown, white. . . . . . . . . . . . . – Christian Science
Copper antique. . . . . . . . . . . .#122
Gray-bronze.. . . . . . . . . . . . . #90 Episcopal
Green.. . . . . . . . . . . . . . . . #70
Green-blue. . . . . . . . . . . . . . #73
Green with brown highlights . . . #6
Green, pale.. . . . . . . . . . . . . #85
Metallic bronze.. . . . . . . . . . . #74
Red bronze. . . . . . . . . . . . . . #65
Red-brown, pale.. . . . . . . . . . . #40

Plated patinas.

Goldplate (even yellow).. . . . . . . #20
Goldplate, deep yellow. . . . . . . . #4
Goldplate, reddish (rose gold). . . #17
Silverplate antique.. . . . . . . . . #12
Silverplate, steel gray.. . . . . . . #42

From the above chart one can observe the preponderance of browns and greens for bronze patinas. A wide range of browns are in an experienced patintaeur’s repertoire. This is due to the nature of copper and its reaction with common patina chemicals. But it should be noted that a wide variety of other colors can be achieved as well.

Further, that plated items (more so silverplate than goldplate) can be given patinas just as can nonplated items and silverplating is infrequently one of the early steps of a distinctive patina. For example, the patina finish for Issue #42 of The Society of Medalists (by Cecil Howard) was first silverplated then oxidized with liver sulfide.

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: https://nnp.wustl.edu/library/dictionary

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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Wayne Homren, Editor

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