Metalcasting offers countless possibilities of interesting projects one can undertake from home. Whether you have a simple electric kiln, or a fancier steel foundry; one thing is essential for all projects involving melting metal: a crucible.
But what is a crucible exactly? It iis any container or vessel used to hold metals as they are subjected to very high temperatures and subsequently melt.
What are the different types of crucible?
Crucibles can be made from a variety of materials. Historically, tradesmen such as blacksmiths and coin minters would use ceramic crucibles made from clay, as the material was very readily available. In more modern, industrial contexts, different kinds of metals are typically used.
These include platinum, stainless steel, carbon steel, nickel, zirconium, and tungsten. Non-metals such as graphite and specialized porcelain are also common. Some more details about these materials can be found here.
What can I use as a crucible at home?
There are a number of items available around the house or the garage that can withstand very high temperatures. Aspiring metalsmiths who are just starting out tend to use things like cast iron pans and skillets, cut-outs of small propane tanks, and other items which resist high heat.
These things can be useful in a pinch, or for some light experimenting, but for more dependable results, it is important to understand the different characteristics of crucibles.
What makes a good crucible?
While there is no clear “best” material for a crucible, certain things can take precedence over others depending on the job. When using metal crucibles especially, there are important things to consider.
Oxidation is a big one. Cast iron and steel tend to break down and oxidize over time, especially when consistently exposed to heat. This can contaminate your metals and produce lots of slag. This is how those DIY crucibles such as cast-iron pans and propane tanks can backfire.
Industrial settings tend to use carbon steels for things such as aluminum handling. But if you know the success of your job is sensitive to small changes in chemistry and molecule breakdown, you should probably opt for the more inert, or noble metals.
These metals, which includes platinum, are highly resistant to oxidation and acids, and thus can last you a very long time. However, some crucibles made from these materials can get pretty costly. Thankfully there is a cheaper and dependable alternative.
Can I make my own crucible?
Yes you can! A great way to economize when assembling your home foundry is to make your own crucible. Ceramic crucibles have been used for thousands of years because of how available and dependable clay is.
Ceramics are extremely resistant to high heat and are chemically stable. Provided you have some clay and a potter’s wheel, you can decide things like the shape and size of your crucible. Ceramic crucibles are a great option for people who are just starting out with their home foundry.
How do I choose a crucible?
With so many factors and some complex science, it may seem a bit overwhelming to select a crucible. Perhaps a non-exhaustive list of important factors will help focus the process. These include:
- The metals you intend to melt
- The temperatures your crucible will be exposed to
- How quickly the temperature will rise and fall
- The type and capacity of your furnace
- Any additives you will use (flux, sand, etc.)
- How you will deal with and remove slag
- How you will empty and clean your crucible
- How many times you intend to use your crucible
- How the crucible will be held/handled (tongs, gloves)
With these specific considerations, you can begin to narrow your research of whatever material you deem best for your project. Some more in-depth information of these factors can be found here.
Temperatures and melting points
Obviously, temperature is a central variable to the entire process of metal-casting. Once you know the composition and melting point of whatever you’re working with, it only makes sense to find the melting point of your crucible.
Here are the melting points of some commonly used materials for crucibles:
|Material||Melting Point °Celcius (°Farenheit)|
|Tungsten||3422 °C (6192 °F)|
|Porcelain||1050 °C (1922 °F)|
|Platinum||1770 °C (2192 °F)|
|Stainless Steel||1400 °C (2550 °F)|
|Nickel||1455 °C (2651 °F)|
|Carbon Steel||500 °C (932 °F)|
|Zirconium||1855 °C (3371 °F)|
|Cast Iron||1204 °C (2200 °F)|
An important note: these temperatures are approximations of the pure concentration of the respective metal/alloy. Many crucibles that are sold are created with mixtures of other alloys and thus their temperature range can vary drastically.
Different types of ceramics can also have varying melting points and integrities when exposed to rapidly-changing temperatures.
You would do yourself best by knowing the exact temperature range of the particular container you are purchasing or the particular clay mixture you are using.
What size crucible do I need?
This may seem like an obvious question and answer, but it is worth clarifying. Metals expand when they are melted, and so you should know the exact cubic volume (determined by weight) of the resulting liquid your crucible will have to hold once the material melts.
Other things to consider would be the size of your furnace, the size of your tongs, and the size of whatever you are casting.
With this overview of the different types of crucibles used in metal casting, you can get a clearer picture of your own home foundry. You should aim to have an arsenal of different kinds of crucibles that are job-specific and dependable.
The crucible is central to the metal casting process and you should take some time to do extensive research and plan accordingly. Look online for others seeking advice for their projects and their backyard foundries, as they can receive some useful answers.
Always make sure to be well-informed in your DIY metal casting projects, and happy smithing!