How To Best Prepare Your Crucible for Casting
Casting metals is the perfect way to create one-of-a-kind projects, from custom pendants to elegant rings. And the star of any casting project is one’s crucible—the clay, ceramic, or metal container that houses your melted metals and alloys.
But any experienced caster will tell you that using a crucible isn’t as simple as dropping one’s metal in and hoping for the best. For the best results, you’ll need to prepare the surface of your crucible’s interior through a process called tempering. Knowing how to prepare your crucible for casting will help you get the most out of your next casting project.
The Importance of Prepping Your Crucible for Casting
Before we discuss how to prep your crucible for your casting projects, it’s important to understand why we do it in the first place. There are two primary dangers of not preparing your surface for casting. The first is related to moisture that may exist inside of your crucible the first time you use it, especially if you’re using a graphite or clay crucible. Water trapped inside the walls of your crucible may flash-boil once you put the vessel on your furnace or torch, which can damage your crucible or reduce its lifespan.
Additionally, tempering a crucible will help keep the melting metal from adhering to the crucible’s surface. Otherwise, removing the melting alloys from the vessel becomes nearly impossible, leaving you with far less metal to work with for your project. Whenever you buy a new crucible, you should take the time to perform this entire process. This includes buying a used crucible.
Preparing for Tempering
The tempering process will involve heating up your crucible, so before you can temper it, you must be sure that it is ready to be exposed to that kind of heat. Here are two steps you can perform to ensure your crucible is ready for tempering.
Cleaning the Surface
Generally, if you buy a brand new crucible, the surface will be relatively clean. However, when you purchase a used crucible, some residue may be left on the surface from previous jobs, and it’s best to clean that off. However, you will want to avoid cleaning your crucible with large amounts of soap and water, as this will add unwanted moisture to your crucible’s walls.
The best way to clean a crucible is to start by scraping off residual materials from the walls. Then, fill the crucible with solid potassium bicarbonate and melt until you notice a red potassium salt later forming on top of the mixture. From here, you should be able to stir the mixture, pour it out, then rinse the mixture with as little warm water as you can.
Whether the crucible is new or used, you will want to eliminate all the moisture from the vessel before you use it. This process is called heat curing, and is fortunately a relatively simple process for ceramic, clay, and graphite crucibles. If you put the crucible in a 300-degree Fahrenheit oven for approximately one hour, it should effectively remove all the moisture from the walls of the vessel. Allow the vessel to cool down on its own to complete the process.
Steps for Tempering Your Crucible
The goal of tempering is to create a thin, protective film on the interior surface of your crucible. This will help keep the metals from sticking to the sides. You can create this film without buying too many additional supplies.
Heating your Furnace
The first step to tempering involves heating your crucible with a hand torch. Not all torches will get hot enough for this purpose. A hand torch from the kitchen likely won’t be powerful enough, but an oxygen-acetylene or a plumber’s torch should work. Heat the surface until it just begins to glow red when exposed to the flame for prolonged periods.
The film itself will be created by a half-and-half mixture of borax and boric acid. However, you can also choose to use only borax. Very carefully, sprinkle pinches of your mixture into the crucible, allowing it to melt into a shiny film, coating the bottom of the crucible. At times, it helps to allow the borax to sit for a few seconds before applying the flame directly to it to avoid blowing the dust out of the crucible with the torch flame.
If you are tempering a larger crucible and don’t want to add the borax by hand, there are alternate methods of applying the coating. Start by filling one-third of the crucible with borax and then placing it into your furnace. Wait until the borax is completely melted before cutting the heat and removing the crucible with a pair of tongs. Then, very slowly, rotate the crucible while the borax is still hot so that it completely coats the inside of the container.
All forms of casting are prone to producing fumes that can be problematic if they accumulate in a workspace—and this includes tempering. Be sure you are in a well-ventilated area before you begin tempering your crucible,
How Long Do I Have To Wait Before Using the Crucible?
The nice thing about tempering is that once you have performed it, you will be able to use your crucible right away. Just be aware that using the same crucible for different types of metals is ill-advised because you run the risk of cross-contamination for the products you make in it. If you want to melt different metals, consider purchasing and tempering a silver-casting crucible.
Other Considerations for a Long-Lasting Crucible
Tempering a crucible will help preserve the integrity of the vessel, increasing its lifespan. However, it isn’t the only way to ensure your crucible lasts. Consider these other crucible care tips, such as:
- Avoid stacking crucibles inside each other
- Choose the right crucible material for the project
- Don’t put crucibles directly on the ground
- Store crucibles in clean, dry spaces
- Always preheat crucibles before use
At Cutting Edge Supply, we know that you care about making sure your casting equipment lasts as long as possible. That’s why we supply casters with all the tools they need for their next casting project.