The Way That I Cast: Lost Wax Process Part 4

Last time we created the actual molds that are used for casting, and we poured the molten metal into them. But what happens now? Well, they need to be quenched.

Quenched? Yes. The metal needs to be cooled down the rest of the way so that it can be handled, and it needs to be removed from the plaster in the flask. Quenching accomplishes both of these things at the same time. Here is a picture of my high tech quenching arrangement. I have a bucket of water sitting up on a metal stool. The still hot flask (in the tongs) is lowered into the bucket of water. Sizzle, spit, steam and it all happens. The forceps in my other hand are used to remove the still warm metal from the flask. I set it aside into another smaller container of water while I clean the flask.

quench and reveal

There is always some plaster left in the flask, so I scrape it out with a putty knife and throw it into the other bucket that you can see next to me on the floor. The flask is then scrubbed with a wire brush, rinsed and put on the floor to dry.

flasks drying

And here they are drying! Meanwhile the newly cast piece is sitting in a small container (an old cooking pot) full of water. It is now cool to the touch, and this is what a typical one looks like.

newly cast buttons

Once I am done casting it is time to begin making these messy looking blobs into something worthy of being put in my shop. This picture shows the basic process. First the pieces, in this case buttons, are cut off of their sprues. This process often requires that the metal has to be cut apart in stages so that none of the buttons are damaged. Then the sprues are set aside to be cleaned and the buttons are given an initial tumble to remove any remaining investment and reveal any surface imperfections. Any flawed buttons go into the sprue pile to be recycled later. The remaining buttons are sanded, polished, inspected, and touched up until they look like this.

smaller button picture

The sprues are then cleaned and polished to remove all traces of investment and metal oxides. They are then dried and put away for later use.

I thought it was important to include a lovely picture of me in all of my pouring safety gear. Quite the fashion statement!

full kit

So for those wishing to replicate this major fashion statement…Starting at the top we have a full face shield to prevent burns from splashing molten metal and boiling water. Under that shield we have a high quality particle dust mask. The process of quenching the flasks can put quite a bit of fine particulate silicon into the air, which is very bad for your lungs. The blue jacket with leather sleeves is a welding jacket – doesn’t catch on fire easily and protects from an assortment of hot things. Leather welding apron and gloves complete the ensemble. What you can’t see is loose fit cotton jeans and high top leather boots.

Next time: How I Got Started Casting

The Way That I Cast: Lost Wax Process Part 3

Last time we created a mold by using a wax model and investment. But is it really a mold that we can pour molten metal into yet? Nope! We now need – Heat, Heat, and More Heat!

Right now the investment is still soft and it still contains waaay too much water to be anywhere near molten metal. Most of the wax has been melted out by the dewaxer, but the investment now needs to be hardened, the remaining wax needs to be burned away, and any remaining moisture in the investment needs to be driven off. The way this is accomplished is by placing the flasks into a burnout oven and cooking them for hours. Here is a picture of my burnout oven.

burnout oven

And yes, 947 is the temperature in the oven. This is actually the low end of the temperature cycle, the temperature at which the flasks are held, at the end of the burn-out cycle while they are waiting to be cast. The high temperature portion of the cycle varies, depending on exactly the type of investment that is used, but it is often around 1300 degrees Fahrenheit. The burnout cycle starts slowly, at about 200 degrees and gradually increases. By the time it is at 700 degrees we open all of the windows and doors in the Studio to let the fumes out. Burning casting wax is a truly nasty smell, and not good for you. By the time the cycle is finished and we are at the holding temperature, about eight hours later, the smell is gone and there is no more wax residue left in the flasks. They are now officially molds!

Once the end of the casting cycle is coming to an end it is time to start melting the metal. I have two electric melting furnaces, a small one that uses a removal crucible, and a bigger one, which is called a “tilt and pour” This just means that you pick up the entire furnace and pour the molten metal directly from the furnace into the flasks.  In either case I have to preheat the graphite crucibles in the furnaces, add the new casting grain and the old metal that I am re-melting, and wait. If you peek into the furnace while it is heating, this is what 1980 degrees Fahrenheit looks like.

recently recharged furnace

Once the metal has melted completely, I start bringing the flasks out of the burn-out oven one at a time. The flask is placed on the silicone pad on the vacuum machine, the vacuum is turned on, and the molten metal is poured into the flask. And this is what it looks like.

big furnace pour

The vacuum machine is actually pulling air out of the bottom of the flask, which helps produce better castings. The flasks are removed from the vacuum machine and set aside to cool. Here is a picture of three flasks cooling on a metal cart. They are sitting next to my small furnace.

small Furnace with flasks

This is a great picture because it really shows how you can see what temperature the metal is by its color. The right hand flask is yellow because it is the hottest. The almost black metal on the left is ready for the next step in the process.

Next Time – What Happens Now That We Have Poured the Metal?

The Way That I Cast: The Lost Wax Process Part 2

Last time we discussed the basic processes for creating waxes for casting. And then we asked: So now that we have waxes, what next? We turn the waxes into a mold.

The waxes are “glued” to special rubber bases using melted wax. The process is called sprueing. Here is a picture of the rubber bases, just after they are done being used.

Rubber flask bases

The red area in the center of the bases is wax and the white substance on the bases is investment (we’ll talk about that latter). You can see a number taped to the side of one of the bases in the back of the pile – that is the weight of the base when it is clean (in grams) and has no wax or investment on it.

These bases, with the waxes in place, are slid onto the bottom of stainless steel flasks, which are basically just large sections of stainless steel pipe. Here is a picture of some of the flasks waiting on their shelf to be used. The blue board on the wall is a production board with all sorts of production details for a variety of projects. The strange looking black thing on the left side of the shelf is an old graphite crucible (it is upside down). I sometimes use it to measure the scrap metal that I am going to re-melt in my small melting furnace to make sure it will fit in.

Flasks on shelf short version

Once the base is on the flask it forms a container for the investment. Investment is just a high temperature material, containing silicon, that looks like Plaster of Paris. It is mixed with water in precise quantities to form a slurry. This is how I buy my investment, in 100 pound plastic boxes.

Satin Cast box

Here is my messy bench, just after weighing the investment. No matter how careful you are this stuff gets everywhere, just like flour. Because the investment contains silicon, which is bad for you if it is inhaled, it is important to wear a good quality dust mask. The upside down rubber bowl on the left is used for mixing the investment with water.

investment weighting

Once a lump-free slurry has been created it is placed in a vacuum chamber to remove air bubbles. The square plate on the top of this vacuum machine has a rubber mat that creates a good seal for the plastic dome that you can see on the left hand side of the machine. It allows the user to create a vacuum chamber that removes excess air that has been trapped in the liquid investment during mixing. Bubbles weaken the structure of the investment and also create lumps on the outside of the cast piece.

Vic 9

Once the investment has been vacuumed it is allowed to harden, the bases are removed, and the flasks are ready to be turned into molds. The stainless steel flasks are placed into a de-waxer, a machine which heats the flasks using steam and allows most of the wax to melt out of the flask. Here is a picture of my de-waxer.


This step is where the process gets its name from – Lost Wax. Removing the wax creates a cavity in the investment that is shaped exactly like the original wax.

What Next: Heat, Heat, and More Heat!