How to Cast Brass

Brass is made by combining copper and zinc at high temperatures. Brass can be cast into many things like house numbers, door knobs etc. It can be a bit of a complex process to melt the brass, but casting it isn't too difficult. You just need some instruction.

Method 1

Method 1 of 3:

Preparing to Cast Your Brass

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You'll need rubber, sand, clay, cornstarch, cold water, and tongs. You should have clay equivalent to a quarter of the amount of sand you have, and cornstarch equivalent to one percent of the amount of sand you have. You should be able to buy these materials at a home improvement store.
Anytime you are near or handling hot metal you need to be very careful. Wear heat-safe clothing, not just heat-resistant clothing. That means you'll need to buy heat-safe clothing online or at a local industrial supply store. This isn't cheap, but it is a necessity. ^{[1]XResearch source}
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Get your melted brass. It is assumed you have already melted your brass before you are preparing to make it into something. You melt brass by putting it in a furnace in an iron pan, but it's a complicated process. Learn how to melt brass before you attempt to cast anything.
- To melt brass, you'll need a metal melting furnace and brass items to melt. You also will need a crucible, which is the piece of equipment that holds the melted brass in the furnace, and a skimmer spoon which is used to transport the material.
- Put your crucible in your furnace following the instructions of your particular furnace model, light your furnace, and then start to fill your crucible with brass after fifteen minutes or so. Keep the furnace going until your brass has completely melted. Once you start to see discolored material on top of the molten brass then you'll know your brass has melted. Remove the discolored material using your skimmer spoon and discard it in a box of sand or a heat safe trash can.

Method 2

Method 2 of 3:

Making Your Mold

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1
Make your pattern. Make sure you make the pattern .017 inches (0.0432 cm) larger than the finished casting to allow room for the molten brass. Brass gets smaller as it becomes a solid. Styrofoam is a popular option for making your pattern, or you can use wood if you would rather stick with the classic technique. Essentially what you'll be doing is breaking up a three dimensional object into shapes that will be pressed into sand. The void in the sand will form the solid cast. You can make any shapes that you'd like as long as it can withstand being shoved into a box of sand.
- You're making a three dimensional prototype of whatever it is that you want to cast. If you want to make basic shapes like a simple doorknob, you can design the prototype on your own using some sort of clay or the materials named above. Whittling a block of wood is always a good option too. Otherwise, if you want a more complex pattern, you'll need to buy it. Oftentimes these patterns are made by experienced metalworkers.
You can also buy a casting pattern at a home improvement store if you would rather not make your own.
Mix sand, clay, and cornstarch. Figure out 25 percent of the amount of sand you have in order to find out how much clay to add. One percent of the amount of sand is the percentage of cornstarch you add. For example: 100g of sand = 25g of clay and 1g of cornstarch. You can eyeball this, but you might need to go through some trial and error. Now move your sand and clay into a box.
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Push your pattern into the sand and clay mixture. The idea is the leave indents in the mixture that will hold whatever shape you're trying to make out of the brass.
- Don't leave the pattern pieces in the sand once you have made the holes, obviously.

Method 3

Method 3 of 3:

Casting the Brass

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You're going to be dealing with molten metal, so you better prepare yourself! You'll need heat-safe gloves, boots, and an apron. It's also recommended that you wear long sleeve wool clothing. Don't forget your heat-safe facemask.
Remember to keep the furnace running until you're ready to pour the brass. As soon as you turn the gas off the brass will start cooling. ^{[2]XResearch source}
You generally don't want to pour more than three molds per cast. By this point the brass will have cooled down too much. Transport the brass in the iron pan that you melted it in. Be very careful and pour the brass out using the spigot. Don't rush.
Depending on the size of your mold this will take an hour or more. Don't be afraid to wait a little longer if it still looks molten to you. Brass generally cools pretty quickly. ^{[3]XResearch source}
Fill a large bucket with cold water. It doesn't have to be freezing, but it should be colder than the lukewarm water coming from your faucet. There needs to be a stark heat difference. Now pour the cold water on your hot brass and the mold. Steer clear of steam. The heat difference should crack the mold right off leaving a still hot brass piece.
You need to wait for the brass to cool thoroughly before using it. Even though you've already waited a while and poured water on it, it is still hot. If you don't wait you might burn yourself. Let it sit overnight to be safe.
Even if you waited overnight, it's always best to use your heat-safe gloves when you touch the metal. The brass piece should be easily removable if you cold bathed it correctly. ^{[4]XResearch source}
Whether it's a doorknob or a collectible, it's pretty cool that you just did that on your own. Good job!

Expert Q&A

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Question
What is the best mold material for casting brass?
Alvaro Mendoza, PhD
Metallurgist
Alvaro Mendoza, Ph.D., is a Metallurgist and the Owner of Mendoza Metallurgy in Portland, Oregon. With over 15 years of professional and research experience, Dr. Mendoza has worked in the aerospace industry in forging, casting, metal-making, and additive manufacturing primarily with nickel-based superalloys, titanium and steels. He currently runs a metallurgical consulting and education business that focuses on providing technical expertise to businesses of any size. He was recently featured on a podcast about why metallurgy matters. Dr. Mendoza received his B.S. and M.S. and Ph.D in Materials Science and Engineering, focus on Metallurgy from the University of Florida.
Alvaro Mendoza, PhD
Metallurgist
Expert Answer
Sand casting is the easiest and most accessible option for people—you use a special sand mixture to create a positive pattern of the item you're hoping to cast. There's also investment casting, where you build the mold around the material with alternating layers of ceramic sand (kind of like stucco).
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Can I pour brass into a brass mold?
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No, you should never cast a metal in a mold made of the same grade as the heat will transfer and warp the mold, possibly welding it into one piece.
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Should my mold sand cast be hot when pouring the metal?
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It does not need to be heated, unless it has become wet, in which case you may want to place it in the oven to dry out.
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Tips

Always be very careful while casting the brass.
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This should be done by a person who knows about metals.
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Never try to cast brass as an amateur. You'll hurt yourself.
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