Before we start, I'd like to provide a little background info on what water casting is. Water casting is a technique that has been used by Japanese bladesmiths for centuries. The process involves melting copper (or occasionally other metals and copper alloys like shakudo) and then pouring the molten metal into a pot of boiling water. Within that pot is a taut piece of canvas that catches the copper. The end result is a perfect disk of annealed copper that becomes the starting point of a tsuba (Japanese blade guard).

Step 1: Materials and Tools

Here's what you will need to be able to successfully water cast copper:

*A forge or furnace capable of heating material to ~2100° F, slightly above the melting point of copper
*A crucible of some sort. I will tell how I made my steel one in the instructable
*Copper stock or scrap, for melting
*Flux, I used borax. Charcoal works as well
*Hacksaw, or something for cutting up the copper stock
*Large pot
*Smaller pot that fits inside of the large pot
*Some form of tough fabric or canvas
*Copper or iron wire
*Pliers
*Water
*A stove for boiling the water
*Safety equipment. This is especially important, this technique can become very dangerous, very quickly if you're not careful

Step 2: Prepping the Pots

Start by taking the small pot and draping the cloth over the top of it. I used an old t-shirt as my source of cloth. Cut a piece of iron/copper wire and wrap it around the pot with the canvas on it. Pull the canvas taut across the top of the pot, then tighten the wire with pliers to hold it in place.

Get your big pot and place the small pot inside of it. Start to fill the entire thing with water. Make sure to press out all the air trapped inside the smaller pot, both pots should be completely full of water with no air bubbles left. This next part isn't necessary, but I jammed some scrap pipe around the small pot just so it wouldn't shift around at all. Pop it onto the stove and leave it to boil.

Step 3: Copper Prep

The crucible I used here is really simple to make. Just take a wide diameter iron pipe, screw on an end cap, weld around the seam between the cap and the pipe, and weld on a rebar handle to the side.

Now I went and started filling the crucible with some copper scrap. I started by cutting 3 lengths of copper pipe and sticking them in the crucible. Then I packed in the empty space with scrap copper sheeting. Next, I sprinkled flux into the crucible. When the copper melts, the borax will float to the top of the copper (it is less dense) and will form a layer that prevents oxygen from contacting the copper. This will end up saving a lot of your material from burning off and oxidizing, increasing the amount of usable copper at the end.

Step 4: Melting and Pouring

Turn on your forge a little bit before the water boils, so it has a chance to heat up. Once the water is boiling, turn off the stove and CAREFULLY move the pot of water next to your forge. Now, put your crucible in the forge, and close off the forge's doors, if it has doors. Once you start to see the metal at the top of the crucible liquify, let the it soak for about 1-2 more minutes. This will ensure that all the metal is completely molten, and is hot enough that it won't solidify as soon as it is taken out of the forge.

Take the crucible out, and quickly move to your pot. Tilt the crucible slowly over until a constant, unbroken stream of copper is flowing out. The copper should be poured directly into the center of the small pot.

At this point, a lot of things are happening. For the first ~10 seconds, the water will not even directly contact the copper at all. The boiling water is so close to its vaporization point, that the ambient heat surrounding the molten copper is enough to convert the water into steam. This creates what is known as a vapor jacket: a pocket of steam that surrounds the entire mass of copper in the pot. This vapor jacket slows the cooling of the copper enough to allow it to settle into the pocket of cloth while still being in a liquid phase, and then form a perfect disk. The layer of molten flux rises to the top of the copper disk, and is blown off by the force of the vapor jacket. The canvas does not burn at this point, because it is surrounded by water that keeps it cool and prevents oxygen from reaching it. After around 8 seconds, the copper will become fully solid, and a couple seconds later will not have enough energy to keep the vapor jacket up. The vapor jacket dissipates, often with a loud popping or rumbling sound, allowing the boiling water to contact the copper. Once the water contacts the copper, it only takes a couple seconds to cool it down to the temperature of the surrounding water, annealing it in the process. You can see at the end, the flux is resting loosely on top of the copper disk. At this point, the copper can be easily removed from the water with a pair of tongs or something similar. If you don't have tongs, you can just dump the water out, or wait for it to cool.

Step 5: Finished!

At this point, you have a really cool copper disk! But what can you do with this? This is the starting point for the round cross guards on many Japanese swords, daggers, and polearms, called tsuba. I am planning on releasing an instructable on tsuba making in the future, but I don't currently have all the pictures I want. This is still an incredibly interesting technique that I think is worth trying even if you don't plan on doing anything with the final cast disk.

Anyways, thanks for reading!
I will be releasing an instructable very soon on the Hamon and Heat Treatment of a Japanese Blade.
Also, I found out that a Knives and Blades contest is coming in December, and I am planning something HUGE for it that I think you all will like. :)
In addition to the knives and blades contest, there is a jewelry contest coming up, and I'd like to do something with mokume gane for that.
Let me know what you all think! :)