Gonny just found my old 2003 instructions for making metal masks. I thought I'd post them here.
If you want to see a minute and a half of the process, it's the same that was used to make the gold masks.
I'll also post some photos of my favorites. They're usually the ones where something went wrong.
Why did parts of the mold break away? Don't know, but it look great!
Sure, I'll tell you guys again. With LOTS of detail.
1 Choose the mask. Attach several wax wires to it in places where it will be easy to grind away unwanted metal. Do this to several masks and connect the wires together like tree branches with the masks as fruit. The wires are called "sprues".
2 weigh the sprued masks. Write it down. Go home. You used up all your time spruing the masks.
3 atttach the main sprue (like the trunk of the tree) to a rubber sprue base. This has a cone shape bump in the center and the tree comes out of the top of the cone. The whole tree goes inside a short section of stainless steel pipe called a "flask". The sprue base has a rubber lip around the edge to seal onto the end of the flask.
4) Take the flask and fill it one and one half times with powdered investment. This is a special high temperature plaster. Sift the investment to remove any chunks. rinse the flask and attach it to the sprue base.
5 Add water to the investment to make a pancake-batter consistency. Put it in the vacuum chamber and turn on the vacuum pump to remove air bubbles. while waiting:
6 pour debubbelizer into the flask to wet the masks. This helps prevent bubbles from sticking to the masks. Pour it back into the bottle to be used again on the next batch. Put a piece of masking tape around the top of the flask so the investment doesn't overflow when you:
7 Pour the investment into the flask. It is best if you have sprued your masks so they won't trap airbubbles when you fill the flask. since that's impossible, put the filled flask into the vacuum chamber again and turn on the vacuum again. This makes any bubbles get much larger so they are more likely to escape and float to the top. When the bubbling stops or you get tired of waiting, release the vacuum. Any remaining bubbles will shrink back down.
8 Let the plaster harden, remove the tape and scrape away the excess. Remove the sprue base. You should see a nice cone to pour the metal in. At the bottom of the cone you'll see the base of the sprue tree.
9 go home. You're done for the day. It takes a while for the plaster to fully harden and dry out.
10 Come back to the shop and plug in the kiln. Put the flask in the centrifugal caster and adjust the weights till it is balanced.
11) Put the flask into the kiln, opening downward. Wait several hours for it to reach 1100 degrees. While you're waiting take the weight of the sprued masks ( you can find it right?). Multiply times 9 for copper and brass or times 11 for silver then add 5 grams extra. That's how much metal you'll need. Weigh the metal on your gram scale. If it's copper, strip some wire or sort some old pennies, till you have enough.
12) Wind the caster three turns and engage the locking pin. Put the metal into the crucible. Ready the Oxy-Acetylene torch, stirring rod, flux, tongs, goggles, and gloves. Wait.
13) After the wax and plastic are mostly burnt out and the kiln stops smoking, turn the flask cone-up (with the tongs and gloves, duh) and continue waiting.
Didn't burn the plastic out completely.
14) When it reaches 1100 degrees, wait another 20 minutes then transfer the (bright red) flask to the sling in the caster. Wire it into place to avoid a flaming meteor. Light the torch and melt the metal. Put a little flux on the metal when you start and another pinch when you're almost done. This helps prevent excessive oxidation of the metal. Use the stirring rod to test if the metal is really melted all the way to the bottom.
This is 10% aluminum so it doesn't tarnish. Don't use flux or you'll ruin your crucible.
15) Put the covering board over the tub containing the caster. Rest it on your torch-arm. Reach under with the other hand, take the torch out, release the lock, release the caster arm, pull your hand out and slam the board down before molten metal flies all over you. The caster spins, throwing the metal out of the crucible and into the flask then spinning fast to force it through the holes left by the sprues into the holes left by the masks. Take the board off with your fingers crossed.
16) If everything worked, you'll see that extra 5 grams of metal sitting in the bottom of the cone glowing brightly as the arm spins. If you don't see the button, look around to see where your metal has gone. It often seems to miss the flask somehow. It can burst through the bottom too. There are many ways it can fail.
17) When it slows down, the button will glow less and less, eventually getting dark. Take the flask with the tongs ( you probably won't need the gloves) and dip it into a bucket of water. There will be a satisfying gurgling-boiling sound and the plaster will melt away until the masks just fall out of the flask.
Oxygen attacks the hot metal. It got to the bottom part more than the top so it's both red and brown naturally.
18) With a toothbrush, remove as much of the remaning investment as you can. Put the masks into the pickling (acid) solution to dissolve copper oxides. this turns the black castings into whitish silver or pink copper. If it was over heated, there can be problems like black marks that won't dissolve.
This one was lost down the drain. I found it when I turned on the garbage disposal!
19) cut the masks off the sprues. File, grind and sand away any remains of the sprues. Sand the masks to remove surface marks if you want "shiny". Using the buffing machine, buff away the sanding marks with Tripoli. Bring to a bright polish by buffing with red rouge.
Sprues still attached.
20) If it's a kanohi, you're done. If it's a krana, you have to grind down the mounting peg so it will fit a Toa head. If it's a two-part silver-brass kraata, you are half done and ready to start over at the beginning.
Bimetallic kraata. I sawed it in half, cast the copper part then reassembled it and cast the other half.
Edit: I marked all the expensive equipment in red. This is why you can't do this at home unless you're ready to plunk down some serious $$$.
This post has been edited by Flintsmith on Sep 23 2003, 07:35 PM
Edited by Flintsmith, May 19 2015 - 08:33 PM.