Pewter molds can be cast by many methods- plaster, auto body filler, brass, bronze, sand, charcoal, cuttlebones, soft bone, baked clay, and soapstone. We will use auto body filler for our method. Roll out a 1/2 inch thickness of modeling clay. Push your chosen spoon halfway into the clay with the concave or curved side down. The clay may be need to worked into place in areas so that it is even all the way around. Fill in any gaps underneath to prevent any undercuts. Remove any excess clay. Push two marbles into the clay halfway on both sides of the spoon to serve as mold guides.
It is time to create the sides that will hold your auto body filler. Roll out a second piece of 1/2 inch modeling clay and form a wall or fence around the form. Be sure not to have any breaks or gaps so the filler will not run out. For easy separation, use a mold separator such as grease, green soap, cooking oil, or petroleum jelly. Make sure you cover the form, spoon, and marbles but be careful not to leave any puddles of excess liquid. Be careful not to make any indentations in the soft clay. Don't leave any excess puddles of liquid.
Mix a batch of plastic auto-body filler. Pour the plastic mixture into the center of the mold to a depth of 3/4 inches. Let the filler level off, then pound on the table to release any possible air bubbles. that may have formed. The air bubbles may leave marks on your mold. If you notice any marks, this can be corrected in the next step.
Give the filler a chance to set. Then carefully separate the modeling clay wall from the filler. The clay will easily separate from the filler but it must be washed with warm soap and water, With the spoon in the mold, wash the mold with warm water and detergent. It may be necessary to scrape around the spoon and mold to separate them. Smooth the mold if you notice any rough spots or pits. Now fill any air bubbles with the mixture of auto-body filler mixture.
To form the second half of the mold, you will need use your finished half mold. Place the spoon in the half mold and build the wall of 1/2 inch thick modeling clay around it. Place the marbles into the mold. Coat the inside with the mold separator such as cooking oil. Roll out more modeling clay and once again build a fence around the mold. Mix another batch of the plastic auto-body filler and cover the pattern to a depth of 3/4 inch. After the plastic has set, remove the clay fence from the mold
Here your completed mold is shown. Wash the mold with warm water and detergent. A channel also known as a sprue now needs cut to accept the pewter pour. With a saw or coarse file, make a sprue in one end of the mold. If you make the mold out of plaster, use a plaster knife for making the flue.Let the mold cure for several days before using. If you create a mold from plaster of paris, you should heat the mold in the oven at 400º for twenty to thirty hours This procedure evaporates water from the plaster. Water will vaporize immediately when it comes in contact with the molten pewter which could create flaws in the pour. Plaster when heated like this can become very brittle, so be careful with your mold. Special plaster for heating can be purchased in craft stores.
To prevent pewter objects from sticking, it is best to cover the mold with a carbon coating. You can achieve this by holding the mold directly over the flame of a candle to create a smoke layer. Molds will last longer if they are kept well smoked between castings. With proper care, this mold will make several castings before it breaks down. Clean out the areas of the design of the mold with a toothpick before you make a pour.
When you pour the pewter in the mold, make sure you clamp the two pieces of the mold together with clamps. It is best to work the melting pewter at 650°. Pour the pewter into a one continuous flow very quickly.
After pewter has cooled and hardened, remove the object from the mold with pliers. The sprue and edges can be trimmed with curved tin snips. Work your way down in cleaning off the edges with a coarse file, then a finer file. Surface flaws and rough edges can be removed with steel wool. After filing the rough spots, sand the spoon with 220 grit sandpaper. Repeat with 320 grit sandpaper, and finally 400 grit. Complete the sanding process with coarse steel wool until you finish with No. 0000 steel wool. This gives the spoon a patina that is soft and smooth. You can buff the spoon with tripoli if you want a silver finish.
Pewter can be purchased in ingots in various sizes. Nathan Trotter and Company which has been in business since 1789 in Coatesville Pennsylvania has pewter currently running at $9.90 per pound for amounts under 100 pounds. Colonial Sense lists several suppliers of pewter ingots below.