Developing my stones cast in place method

Test ring -w- rough finishing

Whether they tell you or not, jeweler's test their processes. Sometimes you get lucky and your test pieces are sale-able, sometimes not. This stones cast in place process is not only new to me, it is relatively new to the industry in general. Little is written and what is lacks details, at least as far as I have been able to tell. This posting included! Sorry. As time permits I will try to add more. There is A LOT going on here.

Anyway, testing for this process is essential. So here we go!

Last night I finished the first test of casting some cubic zirconia stones in place. The stones survived, the setting method works, and the stones are very well set. This one has been polished up a little just to get a feel for the look. Of five stones, each set in a slightly different way, two were very good. Two were set in a way that trapped some "schmutz" behind them so they look brown. I had written off the smallest one but it came out pretty well anyway.

Test ring, desprued, & descaled

The photo on the left is of the ring after some quick finishing. I just wanted to get a sense of how the stones might look after a ring is finished. A high polish ends up making some defects more evident. So this is a good way to see what's going on.

To the right is a picture after the piece had been de-sprued and had the fire or casting scale removed. I usually call it "schmutz". Scale is a combination of metal oxides and other compounds that form when the surface of the hot hardening metal encounters oxygen and the compounds in the investment plaster. It is removed by a process involving light acid etching (the pickle), scrubbing, ultrasonic cleaning, and in my case magnetic pin finishing (which is really a tiny, tiny hammering process).

All the different holes were put there in case the casting process failed. Then I would have had to try some mechanical setting methods such as Pave.

Test ring wax, sprued & vented

Here to the left is a picture of the wax which has been "sprued up" prior to investing in the plaster. The red and dark blue sprues & vents are pre-fabricated wax rounds or "wires" sold specifically for this use.

One difference in my casting process is that I use vents and a vacuum process. Most jewelers do not so they can conserve material costs. Instead they rely on either pressure or vacuum methods alone to help the metal flow.
Venting is standard in larger castings such as those for cars, planes, or other industrial parts. Those molds are so large that applying vacuum or pressure in most cases, is not practical.

Venting allows trapped air and the various gases to flow out of the mold directly rather than through the investment material, which is actually fairly permeable to gasses. This helps eliminate the need for pressure to force the metal in to displace the gasses or vacuum to pull the gasses through the investment material.

Of course anything goes. The more expensive and critical the part, the more extreme the process. I have read about but not actually seen vacuum & pressure casting methods used for large parts too.

To me time is money. Venting results in a more reliable casting and less rework. I am also constantly fine tuning my sprue sizes and shapes to improve the casting quality, reduce rework, and conserve materials. Over time this will allow me to pass some savings along to my customers.

I continue to utilize vacuum since the gases continue to form even when the mold is full. Pressure pockets can still create voids and deformations. Vacuum applied to the outside of the investment helps remove the gases & reduce problems resulting from these gases. It's a relatively easy and affordable way to save time and improve quality so why not?

The second test will be tonight with attention to the getting a more finished setting out of the cast directly. When the quality is right I'll start the production pieces.

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