5 Tips for Mass Finishing

There are many paths to the perfect finish. When it comes to mass finishing production jewelry there are a few tricks you can use to keep your pieces looking their best. The following is a series of tips provided by industry experts to keep your mass finishing processes tiptop.

Start with the Wax

“We started a study aimed at improving our mass media finishing of cast items and found that we should have started with a study of how to improve the surface quality of our wax patterns. We found that most of our finishing problems were caused by reproducing wax defects in metal during casting.

“It’s more difficult to see a defect on a wax pattern than on a metal part, and small defects that make a big difference are easy to miss. In the finishing area, we saw little cavities of different shapes. At first we thought they were investment inclusions, but after looking at a lot of castings we realized that the shapes were repeated, and investment inclusions shouldn’t do that. Although the depressions weren’t deep, they required that the surrounding metal surface be removed in mass finishing to blend to the bottom of the defect. This can take a lot of time and might remove details we would rather not lose.

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“By revamping our wax injection area and eliminating these defects at the source, we improved our finishing results and reduced labor.”

– Eddie Bell
Rio Grande, Albuquerque, New Mexico

Garbage In, Garbage Out

“The old adage of ‘garbage in, garbage out’ is never more true than with mass finishing gold and silver jewelry. Prior to putting your castings through a mass finishing process and expecting near-perfect results, make certain that your masters and molds are impeccable, and that your casting surfaces are topnotch. Go over each master to ensure it is blemish-free and there are zero surface glitches. Check the castings to ensure that the surfaces are smooth and also blemish-free.

“Obtaining quality finishes starts with precise temperature control of burnout ovens and melts, as well as using the best casting investment you can find. It is maddening to go though all the steps and time in the actual mass finishing process and then QC the lot only to find simple casting mistakes. So make sure to perform due diligence on the front-end of manufacturing to get the best results at the end of the line.”

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– Marc Robinson
Former international independent representative for
Hispana Jewelry Equipment Supply, Barcelona, Spain

Opt for Rotary Tumbling

“For many applications, a simple, old-fashioned rotary tumbler with stainless steel media is your best mass finishing option. As opposed to magnetic finishing with pins, which at high speeds can mar the surfaces of parts with millions of tiny indentations, traditional tumbling is gentler on castings. Just remember to use media that is larger than the openings in your parts so you don’t wind up trying to remove trapped media.

“Many years ago I learned a trick from Steven Alviti [of Bel Air Finishing in North Kingstown, Rhode Island]: Use burnishing media to rotary finish your parts before using a cutting media. The burnishing action smoothes the surfaces without removing metal, reducing the time required and the metal lost in the cut down step. Later, use the same burnishing media at the final stages of finishing to cut down the time required for manual polishing.”

– J. Tyler Teague
JETT Research, Fairview, Tennessee

Try Wet Blasting

“A method of mass finishing that works exceptionally well but is rarely used in the jewelry industry is wet media blasting, using fine 300 mesh glass beads in wet slurry. Pumping the slurry through a wet blasting machine directly onto a cast tree can help you get into places you just can’t reach with a magnetic finisher. For example, this method is ideal for rings and bracelets that have cast-in-place stones or latticework on the back. Using very low air pressure (under 15 psi) in conjunction with the slurry stream provided by a recirculating slurry pump system, you can blast the parts quickly and efficiently.

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“The microscopic glass beads under water and air pressure brighten the surface much the same as a magnetic finisher would without leaving any dents in the surface. If you try this method, take care to keep the pressure low; higher than 15 psi can tear up the casting surface.”

– J. Tyler Teague
JETT Research, Fairview, Tennessee

Magnetic Rules

When magnetic finishing with pins, follow these guidelines to obtain the best results:

  • Always fill the bowl with about an inch-level worth of pins (just enough to cover the bottom).
  • Use approximately 250 grams of the same size media.
  • Use a low water level (about an inch). The media shouldn’t rise up the side of the bowl.
  • Use a fresh water and soap solution for each new run. Filter used water and put aside for refining.

– Tech Team, Stuller Inc.
Lafayette, Louisiana

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The award-winning Journal is published monthly by MJSA, the trade association for professional jewelry makers, designers, and related suppliers. It offers design ideas, fabrication and production techniques, bench tips, business and marketing insights, and trend and technology updates—the information crucial for business success. "More than other publications, MJSA Journal is oriented toward people like me: those trying to earn a living by designing and making jewelry," says Jim Binnion of James Binnion Metal Arts.
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