VOCABULARY TERM: BUFFING AND POLISHING

Buffing and Polishing. Treating a metal surface, often to give it a smooth and reflective finish, by use of cloth or wire buffing wheels and a polishing compound. Buffing is intended to remove minor surface striations and tool marks, polishing to add color, brightness and luster. Some polishing work can be done by hand, most however is with a motorized wheel, of two or more speeds.

Buffing wheels are made of leather, sheepskin, muslin, felt, flannel, chamois, hard rubber, bristle or wire brush; each has its own polishing properties or applications with certain metals. Likewise, polishing compounds have different properties: crocus, for example, cuts more than smooths because of its coarser grain, while rouge will smooth and create a highly reflective surface. Other polishing compounds are bobbing compound, tripoli, chrome oxide, tin oxide and grease based compounds.

Buffing. All metal objects should be cleaned before buffing, even hot pickling to remove oxides if necessary. Buffing with a power wheel will remove small pits, scratches, flow marks, tool marks and such; however excessive buffing wears away surface metal so operator control is important (an operator does not want to cut groves in the object with the buffing wheel).

Cotton or muslin buffing wheels are used for most medallic work because of the surface textures. Rouge is chosen based on metal treated: red rouge for gold, silver, bronze, copper; brown rouge for pewter, lead, white metal (white rouge is available for platinum or white gold). Buffing wheels come in several widths and knife edge buffs.

All buffing leaves some deposits, most appear black. These need to be removed by rinsing. Dust from the polishing compound is generated around the buffing wheel and the operator must wear a mask. Buffing of enamel is done with wood laps.

Hand buffing for relieving. A paste or slurry of pumice and water is used to buff medals after they have been abrasive blasted and immersed in a darkening solution, like ammonium sulphide, as a step in oxidizing or antique finish. It is used with a wet wheel under moist conditions.

The pumice slurry is flooded over the surface of the medal. The medal is positioned, slightly slanted, below the buffing wheel and centered with it. The medal is rotated by hand under the buffing wheel and raised to come in contact with the wheel. Slurry is added as often as it dries out under the wheel.

During buffing the medal will heat up, often too warm for the fingers, the slurry will help cool it to continue. First one side is buffed, then the other; then the edge; rotating the medal until all surfaces have been buffed. The medal's design will have some bearing on the wet wheel buffing; a rope border, for example, will tend to cause sore fingers that a molded border does not.

Patina polishing. Some surfaces are given a buffing treatment as part of their patina. An example is scratch brush in which a wire brush is used to create the deep satin finish. (Steel or nickel wire wheels can be used, but not brass on silver which leaves a yellowish deposit.) When using a wire brush it frequently needs to be changed direction, as the wires tend to mat down.

For large flat surfaces leather wheel and tripoli will produce satin finish, as will bristle or nylon brush with petroleum jelly or other grease based compounds.

Proof polish. Diamond dust polishing compound is used with a hand grinding wheel to proof polish the area of a die desired to have a proof finish. This is usually done at a bench by a tool and diemaker. The topmost part of the die, is the easiest to polish. This will usually be the background or field for a contrasting proof surface. A coin of full proof finish requires a die whose entire surface is polished with brush wheels and diamond dust compound. Afterwards it is usually followed with a rouge polishing to effect the mirrorlike die surface which has – and will strike – a surface of high reflectiveness.

Jewelry finish polishing. Some medal designs have polished areas in contrast to satin finish for the rest of the surface; such polished areas include edges, lettering and some relief. This is called jewelry finish, typical of techniques used in the jewelry manufacturing field. See polished edge.

Polishing silver. Silver objects take on a distinctive finish from polishing: light polishing over the lifetime of the piece – creating "butler's finish" – is highly desirable for some silver pieces (notably tableware and flatware but not for numismatic items!). Such a polish gives a deep tone to table silver, prolongs its life, eliminates any start or extension of tarnish and actually is a series of microscopic ridges in the surface. White gloves should be worn when a person polishes silver, this prevents perspiration from contacting the silver, lodging in the minute ridges; this is a start of detrimental tarnish and is a detriment to a perfect polish.

Polishing small silver objects – like coins and medals – will remove delicate relief and is not recommended. High points of such items are also vulnerable to such polishing. Polishing should not be done by anyone, particularly inexperienced persons.

To read the complete entry on the Newman Numismatic Portal, see:
Buffing and Polishing (https://nnp.wustl.edu/library/dictionarydetail/515374)

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