Playing with Fire…Lost Wax Casting (Part 2)

Ok this is where it starts to get fun! Not that the first steps weren't fun, but working in wax is a more calm and contemplative type of fun. In these steps you get to use a big torch and just blast the metal until it is molten hot and ready to cast. Truth be told, this part makes me really nervous because there is not that much margin for error and it is harder to fix or undo any mistakes. I still require my teacher Kathy to literally hold my hand right before we let the arm of the centrifugal caster go. It is nerve-racking stuff and I normally forget to breathe during the whole process (probably not my best idea when wielding a big torch!). Ok, enough about my fears and anxiety! Lets get started!

Investing

Now that you have your wax piece good and sprued (ok, I know I am immature, but the word sprue is kinda funny!), attached to the sprue base and have fit a metal flask on top it is time to invest. I forgot to mention that is is important to weigh your wax piece after it has been sprued (hehehe) in order to estimate how much silver or other metal you will need for casting. It is super annoying if you have already painstakingly attached your wax to the base and realize you forgot to weigh it! Grrrrrrr....

Now investing.... The investment used in jewelry casting is kind of like a plaster of paris that dries/sets up quickly and will eventually harden around the wax original in order to create a mold. Once the investment hardens you can yank the sprue base off to expose the little holes made by the wax sprues.

Investment sprue

Here is a better picture of the holes made by the wax sprues. The next step will be to put all the flasks in a kiln and burn out the original wax (thus the name "Lost Wax"). The wax sprues that were so carefully planned out and attached to the wax original will act as channels for the molten metal to flow through during the casting process. We now are getting close to the fun part (or anxiety inducing if you are me).

 

Centrifugal Casting Machine

The picture to the right is of the centrifugal casting machine I use for my cast work at the Clear Creek Academy of Jewelry and Metal Arts. The blue discs at one end of the casting arm are used to balance the arm and can be adjusted when casting lighter or heavier pieces. The little white cup looking thingy near the middle of the arm is called the crucible and it is where you will melt the silver for casting (you can see my silver scraps already in the crucible). On the far end of the arm is where the flask containing your mold will go. Before casting, the flasks are all kept hot in the kiln.

Ok... This next part goes pretty quickly and it is probably more interesting to just see step by step pictures instead of me boring you to death by explaining everything in painstaking detail.

Torch Flame

#1: The arm of the casting machine is spring loaded, so you will first need to wind up the arm and lift up the pin to set it in place.

#2: Put your metal in the crucible and blast it with a torch! The point is to get your metal to a molten state as quick as possible (without boiling it, which is bad!).

#3: Once your metal is good and molten without any chunks, pull your flask out of the kiln and set it in the metal holder. (seen in the far end of the photo)

 

Casting Spinning

#4: Keep the torch on the metal until the very moment you drop the pin and let the arm fly. The centrifugal motion of the arm will draw the molten metal into your flask. This is where you just hope and pray everything will work out for the best!! In this picture you can see the red blur of the molten metal.

 

 

 

 

#5: Let the spinning arm slow down and pick up your flask with a pair of tongs and gently set the flask down on a fire brick.

 

 

 

 

Hot Button#6: Here is a picture of the flask right after casting. You can see the silver button is glowing red hot. The button is made up of the remainder of the metal that didn't flow into the mold and helps to evenly cool the silver in the flask. The button is also a good indicator of how hot the metal was when it flowed into the flask. If the edges of the button are rounded, then the metal was on the cooler side, versus, if you can see some "flashing" or metal that looks like it has splashed up on the sides of the investment, then the metal was a little on the hot side! In this picture, it looks like the metal might have been a little hot! Oops!

 

 

#7: Once the button is no longer red hot and you have let your flask cool for about 15 or so minutes you can quench it in a bucket of water. The flask will make a really satisfying sizzling sounds as some of the investment is boiled off. If you are lucky most of the investment will boil off when quenched, but if you are extra careful and wait too long you will have to dig your now silver piece out of the investment.

 

 

 

 

#8: Here is a picture of a pair wedding bands that I had made for some friends. The surface of the silver is black because of the oxides that built up while heating the metal during the casting process. I will dig out the rest of the rings from the investment and then use some small dental tools, a pallet knife, and a soft tooth brush to get the rest of the investment off.

 

 

 

 

In this picture you can see the two rings and the sprues (that are now also cast in silver). Once I have cleaned the investment off the piece I will plop it into a heated solution of "pickle" (an acid based solution that will remove the surface oxidation on the silver) and then I will start the process of cutting off the sprues and polishing the piece!

 

 

 

I think that is a good place to end for now! I am impressed if you are still reading. At this point you might be thinking, why would anyone do this?! I don't know if I really have an answer for that, but for me, it is so satisfying to see something you created from scratch transformed into a precious metal. I also like the various steps it takes to make a piece because that means that you don't spend hours and hours just doing one thing (even though I do sometimes feel that way when I am polishing my pieces for an infinite amount of time). So if you can bear it, the next post will be about the steps required to finish a cast piece. Please also keep in mind that I am in no way an expert on this subject, but I feel it is important to explain the work and effort that goes into making jewelry by hand. I also tend to be a creative speller so please excuse any obvious grammatical or spelling mistakes! I hope you learned something and thanks for sticking with me on this post!