Remember this?
Part I of this series can be found here.
Part III of this series can be found here.
The molds that we left in the steam de-waxer have lost more than 90% of their wax. They are now ready to enter the next phase of casting! Here is the de-waxing machine:
Not very impressive by itself. Here is the inside, after a de-waxing. Note the residue of bright red wax on the grate.
We are in the process of changing over to a nice shade of blue, it will be interesting to see the color layers after that!
Here are some of the various alloys we use. Different levels of hardness of white gold, a fine blush rose gold is visible there in the background, and a rich yellow 18k alloy are just a few. The pure metal is stored in a time-release safe, and will be counted out, grain by grain, measured, and calculated with the appropriate alloy.
The burnout kiln stands at the ready. This one is capable of a timed temperature ramp, up to appx 2000˚F.
Inside the kiln. Not only will the extreme heat (1350˚F) vaporize what little wax may be left, the heat will also serve to harden the investment, bringing it to a pottery-like density that can withstand liquid heavy metals sloshing down into the cavities.
Tools stand at the ready. We use a welder’s torch, but have also used an electric melter in the past. The white bowls are crucibles, the black rods are graphite stirring rods, and bin at the back is casting slag.
Jason has pre-heated the kiln, and now places molds in very carefully. At this point, they are at their most fragile- the wax is gone, leaving thin pieces of plaster investment in between details. The investment has not yet baked to a hard consistency. The slightest jar can knock shards of investment into the mold, which metal will not cast over. This will leave literal chunks missing from the final cast design. Not only are they fragile, they’re hot!
8-10 hours later…
Here is our alloyed white gold (not this ring, but the same cast). Gold always comes from the ground yellow, but can be alloyed into white, rose, or various other shades. The alloys you see here are primarily nickel, silver, bismuth, and palladium. Stupidly, I failed to get a shot of the raw silver alloy
The vacuum caster stands ready. We used this yesterday to de-air the investment, remember? Our company used to utilize a centrifugal spin caster, but the vacuum casting setup takes up less room, so we went with that option, for now. Vacuum casting is also somewhat safer, as there is no chance of hot molten metal slinging around the room!
What is this unsightly thing?
Why, it’s our custom made ventilation hood- drawing out toxic fumes from the vaporizing wax, gases from the melting metals, and the stifling heat.
Jason fires up the torch and applies heat to metal.
I love this photo:
More heat, a pinch of flux, and a stir with a graphite rod…
The flux is a cleanser for the molten metal, not only bringing impurities to the surface, but also acting as an oxygen barrier. Primarily boric acid and powdered glass, flux comes in a light dust that must be mixed with the melting metal.
The flask is fit snugly into the machine, all seals are checked, and the vacuum is switched on. Our machine pulls 29 inHg, sucking air out through the finely porous investment.
Pouring the metal:
This must be done when the metal is at the perfect viscosity and temperature- too hot, and the alloys will begin to smoke off, too cold and there will be an unmelted sludge of alloy that is not mixed into the gold or silver properly.
A perfect ‘button’
The button is that glowing nub of metal you see here. It is the extra weight that helps drive the molten metal into the crevices of detail. The metal is still glowing because it is still about 1100˚F.
Sixty seconds later, the button is cooling and I somehow lost camera focus:
The hot flask is set in our far back room to cool. It makes a lovely ‘crink-crink’ sounds as the temperature drops and the metal shrinks.
The last step:
Jason cleans out the crucible. A quick blast of heat melts the vitreous flux, and any tiny droplets of metal left behind fall out. The crucible is now ready for the next batch of metal!
Part I of this series can be found here.
Part III of this series can be found here.
For more photos of this process, visit our flickr photostream!
