Form your figurine from sculpting wax, available at art supply stores. Dentist picks, small flathead screwdrivers and thin knives all make good wax sculpting tools if you can't find tools made for the job. Heat the tool tips over a candle's flame and use them to carve the wax, or warm small amounts of wax in your hands and build up the figurine. Use the tools to add any surface texture you want to appear in the pewter figure.
Obtain sprue wax from a jewelry supply store in 1/2 inch and 1/4 inch diameters. These wax rods form the tunnels that will carry the pewter through the mold to your figurine. Cut the 1/2 inch rod about 4 inches longer than the height of your figurine and bend it into a slight "J" shape. Lie your figurine on a table and align the J so the top is about 2 inches higher than your sculpture and the "J" curves below it. Attach at least two 1/4 inch rods curving upward from the bottom of the "J" to your figurine. Attach one near the middle and one near the top, plus extras for any narrow areas such as arms. Try to attach them to areas with little texture. Attach a final 1/4-inch rod to the highest point of your figure and cut it even with the top of the "J."
Weigh your figurine on a dietary scale, including the sprues, and write down the weight, rounding up to the nearest ounce.
Lay your wax on a metal tray, such as an old cookie sheet, and mix up a small amount of plaster of Paris according to the package instructions. Wear latex gloves and sift the plaster into the water, then mix the plaster with your hands, breaking up any lumps with your fingers. Before the plaster hardens, flick the plaster liquid onto your figurine until one side is coated, then turn it over and coat the other side. This is called the "fine investment" and will pick up the detail of your figurine's surface, so make sure it is fully coated.
Select a container large enough to hold your wax with at least an inch of clearance on all sides, including the bottom. Mix equal parts plaster, sand, clay powder and water in that container, stirring well. Before it hardens, sink your figurine, coated in its dry fine investment, into the mixture, using rubber-gloved fingers to hold onto the top of the J until the mixture--called the "rough investment"--sets up enough to hold it steady. This should take no more than 15 minutes. Hollow out a little extra room around the top of the "J" and allow this to dry overnight.
Light a fire in a large outdoor fire pit with a fireplace rack (the kind that holds the logs off the bottom of your fireplace) set above the wood. Remove the investment from the container (you may need to cut the container away) and place the container upside-down on the rack. Continue feeding the fire until no more wax has melted out for at least 10 minutes. Let the fire die out and place your investment container right side up on a heat-resistant surface.
Multiply the weight of your wax by 9.5 to get the weight of the amount of pewter you need. Place the pewter ingots or casting shot in a steel container and put on safety gear such as heat-resistant gloves and safety goggles. Melt the pewter using a butane torch, moving in slow circles to keep the heat even. Impurities in the pewter will rise to the top. Scoop them off with a metal spoon.
Lift the steel container with fireplace tongs and slowly pour the melted pewter into your investment in a single pour. When pewter starts flowing out of the 1/4 inch hole left from the sprue on top of your figurine and no longer flows into the hole from the "J," your mold is full. Wait an hour for the metal to cool, then break open the mold with a hammer.
Cut off the sprues with a multitool cutting wheel as close to the figurine as possible, then grind and sand any excess metal down so all you have left is your figurine. Clean away any remaining plaster with water, and use your sculpting tools to pull it out of hard-to-reach areas, if necessary. Dry the figurine and coat it with car wax, according to the product's instructions, to seal the surface.