Porosity and Pits: Why Cast Jewelry Fails Late — and How Fabricated Construction Avoids It

The defect that embarrasses a brand arrives late. The piece passes on the bench, ships, sells — and weeks later a pit opens in the surface where nothing was visible before. Porosity was there the whole time, under the skin of the metal, waiting for polish to reach it.

What porosity actually is

Cast metal solidifies from the outside in. Gas that was dissolved or trapped in the melt has nowhere to go as the structure closes, and the last material to solidify shrinks as it cools. The result is voids — spherical gas pores and irregular shrinkage cavities — distributed through the casting, often a fraction of a millimetre under the surface. On the bench, under a skin of solid metal, they are invisible.

Why it hides until late

Polish removes material. When the polish reaches a subsurface void, the void opens — a pinhole, then a pit, growing with every subsequent finishing pass. The piece did not change; the surface finally arrived where the defect had been all along. This is why a casting that looks perfect at the tree stage can fail after finishing, and why "it passed inspection" and "it is sound" are different claims.

Where designs make it worse

Porosity is a solidification problem, so it follows heat. Thick sections feeding thin ones leave the last-to-solidify material in the worst position. Geometry that traps gas — blind channels, fine texture, sudden changes in section — gives the melt somewhere to put it. The designs most exposed are the ones with the most complex internal geometry, which are often the designs chosen precisely because casting makes them possible.

The fabricated alternative

Wire and sheet stock arrive already solid. There is no melt to trap gas, no solidification front, no shrinkage cavity — the metal's structure was set at the mill, under controls a workshop never has to reproduce. Joints made in solid stock with a clean, tight weld do not reintroduce the problem. For the work we take on, this is the default route: divide the piece, fabricate the sections, join them. The fabrication vs casting comparison covers where each route earns its place — casting remains the right answer for geometries fabrication cannot reach economically, and a workshop worth talking to will say so rather than sell one route for everything.

If your design must be cast

Keep walls uniform and avoid thick-to-thin jumps. Allow a finishing allowance so polish has material to remove before it reaches anything unsound. And ask the foundry about their process controls — how the melt is handled, how gas is managed, what they do when a tree shows defects — because the quality of those answers predicts the casting better than any paperwork does.