Pewter Casting

Pewter casting is primarily done using circular rubber molds in a spin casting machine. Metal is poured in through the central hole while the mold spins, and centrifugal force pushes the metal into the cavities along the outside of the mold. In this article, we will give a general overview of methods used for spin casting along with suggestions for further reading.

1. Casting Alloys
2. Contract Casting
   1. Models
   2. Pricing
3. Purchasing Equipment

In order to get started with pewter casting, the first thing you will need is a model. Many artists make their own models, or you can have them sculpted or 3D printed.

Sculptors will typically make the original or “master” model out of clay. Once they have a clay model, they make a room temperature vulcanizing mold or RTV mold as clay will not stand up to the temperature and pressure of standard vulcanizing. Once an RTV mold is made, new models can be cast in high-temperature resin.

This shows the sculpting process of a clay model along with the final product cast in pewter.

With 3D printing, models are made directly with high-temperature resin which eliminates a step in the process. The downside to this is that there will be striped rough marks on the outside of the piece that need to be cleaned off by hand. 3D printed models are good for pieces with smooth sides that are easy to address using sandpaper. If the piece has a surface with a design or a background with sharp edges, it will be very difficult to remove all the rough marks.

Once you have your resin model, it is set into raw rubber and vulcanized. During this process, the raw rubber heats up under pressure to about 350F and liquefies. It conforms to the model and recreates an exact replica of it. After the vulcanizing process, the mold is gated (metal goes in) and vented (air escapes).

From this single-cavity mold, production models are cast. The production models will be used to create a multi-cavity mold that can produce many pieces with a single pour. The production models need to be cleaned up as well as possible because any imperfections will show up in the production pieces.

To learn about making rubber molds and casting your own pewter jewelry or figurines, check out Oster Pewter’s guide to rubber mold making and casting.

When making master models keep in mind that every time you make a mold there is a certain amount of shrinkage. Master models must be large/thick enough to undergo 2 shrinkages. Each shrinkage can be anywhere from 2% to 8% of the metal thickness. The exact shrinkage depends on the type of rubber mold material and the shape of the casting. If you lose your master model and model mold, you may not be able to make a new mold from production pieces because of the shrinkage.

For proper organization, you should always keep your master model, model mold, and production models. Rubber molds eventually wear out, but with a well-organized mold catalog it’s easy to create new molds.

Casting Alloys

Since pewter is an alloy, it can contain varying concentrations of several metals in order to get the desired properties for the type of casting you’d like to do. Currently, we offer 4 different casting alloys with the availability to cast in custom alloys if needed. Below are the four different alloys, what they’re used for, and the elemental breakdown of each.

1. RO7 - 95.75% Tin, 2% Antimony, 2% Bismuth, .25% Cu
   1. Good for: Small, detailed castings that don’t bend easily
   2. Bad for: Large castings or pieces that need smooth, highly polished surfaces
2. RO5 - 98.75% Tin, .5% Bismuth, .25% Copper, .5% Silver
   1. Good for: applications where very soft metal is preferred
   2. Bad for: small or stiff pieces
3. CM8S - 92% Tin, 8% Antimony
   1. This alloy is specifically designed to be mixed with pewter spinning scrap to produce a castable alloy.

To buy pewter ingots for casting, visit our online store.

Contract Casting

In order for us to make pewter castings for you, we will need a mold. If you don’t know how to get a mold, please give us a call, and we will connect you with appropriate partners depending on your needs.

If you have a design that you want cast in pewter, Oldani Brothers can produce it. Please read through the specifications below to understand what we need in order to get started.

Provide Models

• Digital models must be in .stl format.
• Digital models will incur 3D printing and model preparation costs
• Physical models should be made of a material that will not deform up to 400F (metal, glass, high-temp resin)
• Low melt models like plastics will incur extra tooling costs
• During the mold making process, models will shrink between 2-10% twice. Please account for this in model sizing.
• Large models or pieces with multiple parts may incur extra tooling prices

The ideal model is a metal model that is already cleaned and will be the correct size after 2 shrinkages.

Pricing

1. Pricing is determined based on the weight and complexity of the piece.
2. Production mold - $100 - $250 (estimated)
3. 3D printed model plus preparation - $150 - $250 (estimated)
4. There is a $200 minimum order on all cast pieces. This does not include cast pieces in our catalog.

Keep in mind that pricing does vary depending on the complexity of the mold. For more information on Rubber Mold Casting and Mold Making check out this comprehensive guide.

If you would like to hire a contract caster to produce your designs, call us at 203-630-6565 or email sales@oldanibrothers.com.

Purchasing Equipment

Several companies make and sell both new and used pewter casting equipment. If you are interested in purchasing equipment to work with pewter, we recommend talking to the companies below:

• Contenti - Offers mold making supplies, grinding bits, and other tools needed for working with pewter.

Learn more about the uses of pewter

This post was written by Peter Oldani. Find out more about the author.