I’ve been carving waxes of renaissance-themed things. When you carve a wax, It’s pretty-much like any other carving, say wood or stone –
you work away removing material until a satisfying form emerges. Wax carving has an extra option, though – the ability to add material by melting blobs of new wax on. This gives the wax carver a safety margin not available to the marble worker. If you cut too deep, never mind – you can add more wax. If you break off some small feature by accident, it can be welded back in place.
But there’s an extra process that is not usually seen. The wax is going to be embedded in plaster than melted away in a kiln, and metal will be poured into the gap left behind. But how will the metal get in? There must be channels or sprues through which the molten metal can enter, that will take the metal to all the right places and make sure that everything gets filled – by no means a certainty.
Here are a couple more waxes for pendants, where the sprues can be clearly seen.