Hi guys!
I’ve been casting with a spin caster a 18k gold wishbone and I keep running into the same problem over and over. I get a clear and full cast at the bottom of the mold but the top (closest to the pour hole, the metal doesn’t fill. Does anyone have any suggestions as to why this happens? I’m a new jeweler and trying to teach myself but I can’t quite figure this problem out.
Any insight is so helpful! 
Thanks so much!
Ava
Hi Ava;
Unless you noticed molten gold flying out of the mold and depositing itself on the inside of the centrifugal caster’s shield wall, it sounds like you’re not using enough gold. To get a good cast, you need to use enough to fill not only the piece (the wishbone) but also the sprue button (that conical thing at the top of the mold). The button provides a reservoir of liquid metal that the cooling metal in your piece needs to draw from as it cools and shrinks, in order to assure a solid casting.
Use a sensitive scale to weigh the wax, including any sprues and the button. Multiply that amount by 14, if you’re casting 14k, or 16 if you’re using 18k. - that’s the amount of gold you need to melt.
Andrew Werby
Juxtamorph.com
Put vents in the furthest points in the mold. It sounds like you have air coming back into the pour.