Sunday, April 10, 2016

Taking the Holes Out of Porosity

I came across a fairly recently cast ring the other day for evaluation (insurance purposes). As I was assessing its quality, I noticed some visible pits on the shoulders and on the prongs of the ring that I thought warranted some discussion with the client before going on with the appraisal. I already knew what this was, but there was something he could confirm for me. When I got a hold of him, I asked if the jeweler had done the work quickly. "Oh yes, he answered. Turned it around in less than a week for me!''. Bingo. This client had a classic case of porosity on his ring, very likely due to the casting which was done too quickly.

In more extensive cases such as this one, porosity can compromise the structure and the setting of the item, and would require recasting. Photo courtesy of  

What is porosity exactly? If you've ever made a cake, you'll know there are ingredients used to make bubbles in the batter that allow it to rise. While this is done intentionally in cake, it is not in jewelry. In recent years, casting precious metals into molds and waxes has become the most popular form of manufacturing jewelry. Roughly 95% of gold jewelry is produced this way and I can understand why: it's cost effective, less labor intensive, and successfully replicates designs (which is perfect for ring refurbishment).  
An example of surface-reaching pits. Possibly just superficial porosity. Photo courtesy of
The downside to this method is that the high temperatures used to obtain molten metal also allows the metal to absorb gases (usually hydrogen). If the work is too hastily cast and forces are not applied to drive these bubbles out, the bubbles get trapped in the cooled material. Mild pits in jewelry are in the best of cases a blemish  that can be repaired fairly easily. In extensive cases which involve full bubbles, cracks and folds, or where these pits or bubbles have gathered in crucial structural parts of ring, this can be a sign of a structure that is inherently weak and may break in time.

Filling porosity pits in a ring. Photo courtesy of

A proactive solution to porosity is also to avoid using wax molds such as this one which have defects which can in turn produce cavities in the finished product. Photo courtesy of
So what can be done about porosity in jewelry? Well this is all really dependent on how extensive the porosity is. If there are only superficial blemishes like pits, some jewelers will elect to fills the pits by soldering gold into them and then to rebuff the overall piece. If it's uncertain how extensive it is, the prudent jeweler will propose to recast the jewelry altogether. My personal experience has been that the reputable jewelers that detect these defects in their jewelry will opt for the recasting, as it means peace of mind for both the jeweler and the client. As for my client from earlier, I proposed that the client see his jeweler to make these changes before appraising his ring. His jeweler took care of it free of charge.
Have you ever experienced this kind of issue with your jewelry?

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