Highlight, Highlighting. Creating a contrast of light and dark areas on a metal surface. Highlighting a medallic item puts dark coloring in crevices and some low areas of the relief, and, by burnishing or buffing, making the higher areas lighter in color. The relief stands out because of this two-toned effect, the contrast aids the human eye in perceiving the total view. Highlight is the result of oxidation (actually a sulphatization) and this relieving.Most patina finishes will employ some form of highlighting and this is a major function of the finishing department. There is no highlighting in coin finish, as coins and tokens receive no finish after they are struck; for most medallic work, however, it is the next important step after the medals are fully struck, trimmed and edgemarked. How medals are highlighted. Medallic items come to the finishing department in tote boxes, they are fully struck up and edgelettered – all the steps of the pressroom are complete including trimming and any edge treatment. The medal at this stage is called a raw medal. The first step is an abrasive blasting with very fine abrasive particles, as sand or glass beads; this gives the raw medal surface a "tooth" to accept further finishing treatment, particularly with fluids. Actually these microscopic pits are called cups to retain the liquid.The abrasive is grossly removed, by shaking off all loose particles, the medals are then placed into wire baskets and doused into a darkening solution (as ammonium sulfate). Immersion time is critical, being removed quickly after the desired darkness has occurred, the medals are then thoroughly washed to stop the darkening action by immersion in still water or running water or both. This washing also removes any residual abrasive particles.At this stage the medals are totally black or as dark as desired – one color. They are brought to a workbench where a wet wheel is located. A medal is covered with a pumice slurry and buffed on the wet wheel to remove the dark toning on the high points, on flat surfaces and all areas coming in contact with the buffing wheel. The dark color remains in the crevices and near some relief where it outlines and thusly emphasizes or highlights the relief. This forms the two-toned effect.Afterwards the medals are washed of all pumice and dried; at this point they are even baked to remove all possible moisture, then lacquered. Some highlight action may continue under the lacquer; such residual toning can be observed in about six month's time and continues, possibly, for several years.See finish and finishing.
excerpted with permission from
An Encyclopedia of Coin and Medal Technology
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON