Casting lighter weight, heirloom-quality platinum designs

By Platinum Guild International and Jurgen Maerz

(Originally published August 2010)

As Platinum Guild International (PGI) USA looks to the future of platinum jewelry in the U.S., it has identified an incremental business opportunity for more accessibly prices “entry platinum.” By broadening the availability of lower prices platinum bridal—including semi-mounts and complete engagement rings under $2,500 (retail) and wedding bands under $1,500 (retail)—and fashion jewelry under $3,500 (retail), PGI is inspiring the industry to innovate in design to create new pieces that will expand platinum’s retail footprint. “Platinum will always hold a strong share of the higher ticket bridal business, but research indicates an unmet consumer market for ‘entry platinum’ that is currently being lost,” says Huw Daniel, president of PGI-USA.

A major consumer study commissioned by PGI in 2009 and conducted by Galileo revealed the purchase process for consumers owning white metal bridal, both platinum and white gold:

• The biggest group of consumers, 40 percent, started out considering both platinum and white gold; however,

• 50 percent of the engagement rings ultimately purchased were in white gold.

• The white gold purchaser holds platinum in high esteem, considering it to be a premium product. But the majority default to white gold in their final purchase because they could not find platinum bridal jewelry within their reach.

To satisfy consumers’ needs for more affordable platinum product, manufacturers can consider many techniques, including reducing diamond content and using new materials and technologies that can help them create durable heirlooms. The use of CAD/CAM with new rapid prototyping materials makes it possible to produce long lasting platinum pieces with thinner walls—and the great strength of platinum allows for these more affordable designs to be structurally sound.

The Casting Experiment

So how do manufacturers create lighter weight, heirloom-quality designs in a cost-effective manner? A team led by PGI technical expert Jurgen Maerz set out to conduct a series of experiments using some of the newest rapid prototyping and rapid molding equipment on the market. The goal was to duplicate designs of remarkable complexity that would be impossible or extremely time-consuming to create using traditional methods. For the purposes of this trial, they used the Envisiontec Perfactory Mini Multi Lens rapid prototyping system and the HD pattern material developed by Victor Joyner and distributed by numerous industry suppliers. There are other systems on the market designed to enable rapid manufacturing, and jewelry manufacturers should explore their options and choose the system that best suits their needs.

In the following sections, the researchers present their process and the results of their experiments:

DESIGN. To begin, we designed three pieces for the study in CAD. This technology enables weight control by calibrating metal thickness and stone sizes. In the three project examples shown here, we were able to achieve the following total platinum weight per piece in pennyweights (dwt) and diamond weight per piece in total carat weight (tcw): basket pendant 0.97 dwt, 0.42 tcw; engagement ring 3.92 dwt, 0.34 tcw; squid pendant 1.45 dwt, 0.02 tcw.

CAD also aids in the setting process, enabling the user to shape the beads that hold the stones in place to the exact stone dimensions. In the engagement ring example shown here, the bead shape is actually a stem with a small ball on top; once the piece is cast, the stones can be snapped into place and tightened simply with a beading tool. No seat cutting is necessary. This greatly reduces labor costs and manufacturing time, and contributes to the lower price point of the piece when compared to traditional setting techniques, which are more labor intensive and can result in additional metal loss.

MODELING. We exported the CAD files to the Envisiontec machine, which grew Photosilver models. Photosilver is a new nano ceramic-filled photopolymer material that can be tumbled like silver to obtain a smooth, polished surface, thus replacing the need for a silver master. The Photosilver material can also be electroplated without deformation using gold, silver, or bronze to achieve the look of a finished piece.

In this experiment, the Photosilver models were hand-finished and molded in clear silicone room-temperature-vulcanizing (RTV) mold rubber. We found this to be a time-saving and rapid way to create a model that is similar to a metal master but does not result in metal loss. This type of model also enable us to get high-quality reproduction of detail when molding in RTV.

MAKING PATTERNS. Once the master models were molded in RTV, we had to produce the patterns for casting. Instead of using traditional injection wax, which for the pieces at hand may not have provided the detail required, we opted for liquid high definition mold media (HD), one of the newer materials on the market designed for the reproduction of intricate details. When using the HD material, there was no shrinkage from the Photosilver model to the mold to the casting, and all of the important details remained calibrated and true. This is especially critical when it comes to stone setting. When using HD material, the stones that are determined in CAD to fit the ring snap right into the finished casting, even though the piece has been molded.

We injected the HD material into the RTV molds, cured it, and removed it in preparation for casting. The patterns were easy to remove from the RTV molds without distortion or breakage.

CASTING. We cast all three of the trial HD patterns directly in platinum950/ruthenium. We feel this is the best platinum alloy on the market today for this application. It is universal in its usability, has excellent hardness of 130 HV, and has a very white color. There is no oxidation after casting and it finishes and polishes much better than softer platinum alloys. For example, platinum950/iridium, which has a hardness of 80 HV, is not suitable for many castings that are thin and lighter weight, as it can deform and dent because of its softness. It is also more difficult to polish for the same reasons.

The pieces were cast centrifugally in high-speed colloidal silica-bonded phosphate investment. We achieved a high degree of detail and minimal finishing was required. You can see this exemplified in the milgrain replication on the ring and basket pendant, as well as one of the suckers on the squid tentacles. Traditional molding and wax injection would not have preserved the detail or dimension of the original Photosilver masters. Six separate shrinkages take place in the traditional sequence to manufacturing—from wax master to metal master to mold to wax injection to casting to finished piece. In the method used here, there was no shrinkage between the original model and the casting.

Our experiments show that this method of rapid manufacturing is superior to the traditional wax method for lightweight, delicate platinum pieces that fall into the “entry platinum” category. Consumers need to be made aware that platinum jewelry is not unattainable and expensive. Small modifications in design and structure can go a long way to making more affordable platinum jewelry available to the public. With modern jewelry manufacturing technologies, platinum can be designed and created to meet every budget.