Note that there are different methods and varying equipment that can be used for casting. This is just one way, and not a comprehensive guide!
Working with wax
Wax work has so many possibilities that it is a bit overwhelming. There are different types of wax, some are stiff and hard, some of soft and easy to shape with your fingers, but attract dust and other particles because of their stickiness. You can melt, carve, saw and file wax. You can melt it and pour it into silicone molds. In the picture below there are some blue wax pieces, for instance the flowers and the small cedar branches, that have been made with wax that is molten and then poured into a mold. When set, this wax is very bendy and plasticky. The smooth looking blue rings are the blue type of wax used for making rings. They are sold as tubes; I sawed a number of rings from the tube and then carefully melted them with a torch. If you heat them too long, everything will melt into a puddle, so take a break sometimes and let everything cool down.
|Wax shapes: the red in the back is soft, sticky wax, the blue is harder.|
Notice the sticks that make all the wax shapes look like weird lollipops. This is a different type of wax that is used to build the tree (aka sprueing). Below you can see the start of a tree and the finished tree on the lid of the cylinder. Building a tree is tricky. I had many pieces, and two trees to build, so I wanted my trees to be as tight as possible. If you look at the very first picture again, you see I have some of my smallest pieces on their own little tree, which can then be set on the top of the big tree. You need about 1 mm of space between pieces, so it can be built pretty tightly. But if pieces fall off during handling, it can be difficult to repair a tight tree.
Note that I cut down all the pink wax sticks as far as possible so save both space and material. Every sprue you add is a piece of silver, so it adds to the weight and cost. Cutting down sticks of wax is always best done with a heated scalpel. Keep a small candle on your work surface to heat the knife, and paper to dry off the wax that accumulates on the blade.
|This is precision work. It's helpful to hold |
the tree in tweezers and fix it as well as possible while working
Once you have weighed your tree you can fasten it to the lid, again by melting the areas that are going to be in contact, both on the wax that is on the lid of the cylinder and on the bottom of the tree. Hold the tree steady while it hardens, and then it is done. If you're experienced, you might want to put the tree at a slight angle if you have bulky items that come a little too close to the wall of the cylinder. This way you can cheat a little and gain a little extra space.
|A finished tree. Note that the trunk is |
very short now. You only have as much
room as your cylinder is high (a little less actually)
|Finished tree seen from above|
|Tree inside the cylinder|
Removal of wax and preparation for casting
The wax is removed (burnt out) from the cylinder in a kiln at about 600C for 3-6 hours. My teacher had the cylinders standing at 600C just before casting, so they are hot and the heat will help the silver stay molten.
Sterling silver scrap is cut into approximately equal parts, to help with melting. If a piece is not molten it will stay in the crucible, so it's not the end of the world, but you don't want that to happen to too many pieces.
The crucible is filled with the silver scrap and the cylinder is put in place in the centrifugal casting machine. And then the hot phase starts!
|A big-ass torch, so loud that we needed ear protection|
|Heating the crucible; the cylinder is directly behind it|
|Getting hot. The silver is probed from time to time to check if |
everything has melted.
|Almost ready to let the centrifuge force the metal into the mold.|
The rotation stops and now we can remove the cylinder with big tweezers. It is placed on a heat-tolerant surface for about 10 minutes to let it cool off slightly. At this moment the silver is still hot and orange in colour. After 10 minutes the cylinder is lifted from the surface, again with tweezers and gloves (still hot!) and quenched in a big bucket of water. The plaster will crumble and dissolve in the water, and your silver tree can be found in a now almost empty cylinder.
|The hot cylinders cooling off before a water bath|
The plaster sits in all the nooks and crannies of your tree. You can try to remove it as well as possible with tweezers, brushes and water, before submerging the whole tree in pickle. As you can see in the pictures, there is a lot of oxidation that needs to be removed.
|The silver tree right after casting and quenching. It's black!|
|The oxidised tree, some loose pieces (too little silver, so they are not |
attached to the tree, and some pickled pieces in the background)
This is how it looks after pickling: