Pewter is a traditional low-temperature metal-casting material used to make everything from jewellery to goblets. Osso di seppia, which is Italian for "cuttlefish bone", is a common technique used when casting pewter. A two-piece mould is made by carving or impressing an item into the bone, pouring the molten metal, and removing the mould marks and extra material after the metal cools.
Don wraparound eye protection and a NIOSH-approved respirator. Use coarse sandpaper to sand the soft sides of both pieces of cuttlefish bone until perfectly flat. They should fit against one another without any visible light when viewed from the side.
Don heavy leather work gloves. Use a hobby knife to carve a negative impression of your desired item halfway into the soft, flat sides of each cuttlefish bone. Instead of carving the impression yourself, osso di seppia artist Mario Casari says you can also make a model of your desired item and "drive the model into one of the bones, sinking it until it is level with the surface of the bone (for almost half its thickness in the case of a ring). The more delicate and intricate parts of the model should be in the lower part of the bone."
Carve a sprue cup, sprue and vents into the cuttlefish bone. See the fourth photo in the Cuttlefish Bone Casting tutorial for an example of a medallion impression with its sprue cup, sprue and vents.
Use rubber bands or tape to hold the two pieces of cuttlefish bone together.
Don full leathers and a face shield. Use a casting ladle or a small saucepan with a pouring spout to heat pewter to a mercury-like consistency on the stove or with a small, hand-held torch.
Carefully pour molten pewter into the mould. Place mould on a vibrating surface such as a dryer for 30 minutes to help remove any air bubbles in the molten metal.
Cut sprue, sprue cup and vents away using wire cutters. Use a coarse jeweller's file to remove mould marks. Polish item with 000 steel wool and finish as desired,
It is also possible to make moulds for casting pewter using lost-wax casting. Instead of impressing the actual item into cuttlefish bone, a wax model, including sprue cup, sprue and vents, is suspended in a metal container, upside down. Plaster is poured around the mould. The mould is heated until the wax is incinerated, and then molten pewter is poured into the cooled mould. For more information, see the tutorial: Graphics for Casting Pewter Medallions at Quazen.com in the Resources section of this article. The most common form of lead-free pewter today is 95/5 metal, which is the same as 95/5 lead-free solder. The 95/5 lead-free solder can be found at any hardware store. It is generally less expensive than buying pewter from a casting or jewellery supply company.