Plating/Finishing


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	Plating and Finishing

Finishing is critical to the success of any pin or emblem. It is important to choose the correct finish to achieve the desired effect. In jewelry manufacture, this generally is achieved using an electroplating process and is supplemented with additional techniques such as sandblasting or oxidation.

Plating utilizes a chemical bath and electric current to deposit metal onto the base metal piece. Recent technology has resulted in better efficiency and less waste contamination than in years past, but the actual process of turning a base metal part into an attractive “jewelry” product remains more of an art than a science. There are many different plating processes, but for our purpose, we will briefly discuss gold, silver, and antique or oxide plating.

Two very important considerations in the plating process is pre-preparation and cleaning. Pre-preparation consists of the various techniques for removal of extraneous metal and general smoothing of the surface. All surfaces have some high and low areas which although not readily visible, become magnified in the plating process. To smooth out these high and low areas, the pieces can be either “tubbed” or polished.

Tubbing is a process where the pieces are placed in a large cylindrical tub with a composite media. Depending on the amount of smoothing required, various levels of “coarseness” can be utilized. The tubbing machine vibrates rapidlyausing the media and jewelry pieces to rub together. Over time (usually several hours), the pieces become smooth.

For an extremely bright, shiny finish, the pieces can be hand polished using a special felt wheel rotating at high speed. Since each piece is handled individually, hand polishing can add significantly to the cost of the finished items. For inexpensive products, this step is often not economically feasible, at least for domestic production. With hand polishing, we can be selective in the areas to be specifically polished. If the area to be polished is located in a very delicate location, we may “mask off” the surrounding area. This is often used when we have a fine balance between “sand blasted” and polished surfaces, or when two tone plating is desired.

When properly done, the contrast between matte and high polish, or between gold and silver plate is very effective.

Sandblasting is a technique for giving a piece a rough background -- usually providing a sharp contrast with a polished surface. It is accomplished just like the name implies. Fine sand is “blasted” against the metal piece by a high pressure stream of air creating a finely “pebbled” finish.

Cleaning refers to chemical cleaning between the various plating tanks as well as at the beginning and at the end of the process. Generally parts which are delicate, prone to tangle, highly polished, or with stones set are “rack” plated and other items such as medallions or basic pins are “barrel” plated. In rack plating, parts are “racked” or “strung” onto a holder which is moved from tank to tank. In barrel plating, the parts are placed into a perforated barrel which rotates as it is moved from tank to tank. The techniques used in these two methods are quite different. A skilled rack plater may not be effective in barrel plating and vice versa.

Basically, most plating consists of copper plate, nickel plate, and decorative plate. Copper tends to produce a very smooth surface. Nickel provides a bright, shiny, silver-colored surface which can be the final finish of the product or can be a base for a later decorative finish. The decorative finishes are usually gold or silver. Silver is normally overplated wth rhodium (a precious metal) since silver tends to tarnish or discolor very rapidly. Black plating is a variation of nickel plate.

Antique or oxide plating produces a matte finish with a darkened background. The antique look is produced by washing a brass or silver plated pin in a thin solution of black lacquer. The black collects in the recesses while it is drying.

Plating and Finishing