Casting a piece of jewellery is the quickest and cheapest method of making jewellery. The method of lost wax casting can be traced back centuries. However with the advent of computer software to aid in the design of jewellery, you can be a skilled IT technician these days and call yourself a jeweller! Casting usually involves the making (or 3d printing) of a wax model, from which a rubber mould is made. Molten metal is then forced into the mould, to solidify into the mould pattern. This process is used to make jewellery in the least expensive way possible and involves the least amount of skill. Poor casting can result from such things as using too much scrap gold, silver or platinum relative to new metal, a misalignment of the mould, improper use of alloys and poor casting. The result is a mounting that is structurally weak and therefore will not last as long as hand-fabricated jewellery, because the metal is full of tiny air bubbles.
Telltale signs of a poor casting include pits or bubbles (called porosity) often only visible under magnification on the underside of the setting. These indicate a poor casting that will likely not last the test of time. Consequently, the prongs or claws of the setting may be structurally very weak and put the gemstone or diamond at risk of becoming loose or worse, falling out and being lost. Cast pieces tend to have softer edges and less detail because they are mechanically finished as opposed to being finished by hand.
Improperly cast jewellery
Results of Improperly Cast Jewellery
1. Gas Porosity
This may be scattered throughout the piece of jewellery and also may concentrate in corners, such as at the junctions of prongs or in galleries. It shows itself as tiny holes or blotches on highly polished surfaces.
2. Shrinkage Porosity
Generally located in thicker areas of a piece of jewellery, this appears as starbursts or irregular cracks in the metal.
Look for cracks anywhere in the cast jewellery, the result of overheating (or in some cases underheating) the metal.
4. Investment Inclusions
“Chunks” of the white investment powder used in the casting process may sometimes appear on an item. Usually removed through standard cleaning after casting, it leaves behind a square-cornered depression.
5. Pits & Depressions
These include depressions from air holes the wax worker didn’t detect in the wax. If the wax has minute holes when it’s cast, it will absorb investment, ultimately leaving a void in the cast item
Some bench jewellers try to fill porosity with solder, a practice that results in speckled discoloured areas. There is no remedy for porosity; in most cases, the mounting should be remade. It’s important to note, the vast majority of jewellery sold is made this way. Some jewellers will describe their work as “handmade” when in fact it is simply “hand-finished”, ie, it is cast into several components and assembled into a single piece, but cheaper CAD cast jewellery simply cannot be compared to something that has been made entirely by hand. The metal structure is weaker and prone to cracking and breaking over time. Any diamond worth more than £2-3k should be mounted in a handmade setting for peace of mind!