One of my favourite jewellery making techniques is casting objects using the delft clay method.
As a jewellery maker I accumulate A LOT of scrap silver, it’s a pain but when making a piece you nearly always end up with some bits that are too small to do anything with, the great thing about casting is it means I can make use of all these bits and pieces of silver. I also love it because it enables me to create beautiful 3D one off pieces.
Delft clay casting is great if you’ve got an object you need to reproduce in silver, (such as an acorn or a fancy button) you can only produce one cast at a time but the process doesn’t destroy the master so you can repeat it as much as you need. This also means that every cast piece is unique!
While it is handy to be able to cast found objects, I personally prefer casting from wax models I’ve made. I like that every piece I create from wax is completely original and what I can cast is only limited by my imagination.
I learnt to cast by reading about it in my silversmithing books, watching videos on youtube and by trial and error. I thought with this blog post I would include a how to guide on casting, hopefully it will be useful to other makers who want to give it a go and interesting to people who would like to know more about the process.
Step 1. When carving your object out of wax make sure you file and sand it well, any nicks or grooves will come out in your cast version and it will take you longer to buff them out of the silver piece than the wax original. (I learnt this through trial and error!) So far I have only tried carving with Ferris blue wax but there are other grades available and even mouldable wax. You will need saw blades and tools for working with wax but you can get it all at Cooksons. It’s a lot more difficult than you would think to carve a shape out of wax particularly one your happy with but it’s definitely worth persevering.
Step 2. To make your mould you will need some delft clay, a delft aluminium ring, a couple of drill bits, talcum powder, large brush, a steel ruler and a scalpel. First take a couple of handfuls of clay and break it up using the steel ruler, keep breaking it up until all the lumps are gone.
Step 3. Fill the smaller ring with the prepared clay (making sure the lip of the ring it at the top) and compact it down but not too much, then even the top off by scraping the ruler over the top of the ring.
Step 4. Press what you want to cast into the middle of the ring of clay (Im using a wax heart I carved). I usually try and get it so about a third of my master is above the surface of the clay. When your happy with the position of your object brush some talcum powder over the surface of the clay.
Step 5. Screw on the top half of the aluminium ring (making sure it’s aligned properly) and fill it with the rest of the clay. Half fill the ring firs,t compacting it down, then fill the rest of the ring and level it off with the ruler. When your happy carefully unscrew the two ring halves and then gently remove the object your casting from the mould. Be careful when removing your object as it is very easy to destroy your mould, I use a scalpel and try not to disturb the clay around the edge of what I’m casting. If I do happen to loosen any clay, sometimes it can be fixed by just gently pressing it back into place.
Step 6. Take the deeper ring half and gently push a drill bit through the centre of your mould through to the other side. You’ll need quite a big drill bit as you need the hole to be big enough for the silver to flow through easily but don’t make it so big it destroys the shape of what your hoping to cast. Now from the other side of the mould (where the drill bit came out) cut a funnel out of the clay using a scalpel.
Step 7. Still working on the deeper ring half; put 5-6 small holes around your mould (on the inside), I just use a smaller drill bit to do this and scrape shallow channels from the edge of your shape to the holes. The holes are just for the hot air to escape. When your finished you can put the rings back together making sure they are aligned properly.
Step 8. Now the hard part is over and your ready to melt your silver. Keeping your mould close at hand, fill a scorifier thats attached to crucible tongs with your scrap silver or silver grain. You need to use quite a bit as some of it will make up the sprue. Sprinkle over some borax powder and then begin heating the silver (always be safe when working with intense heat and have some water to hand) it may take a little while depending on how powerful your torch is, if you only have access to a small handheld torch you may not be able to get the silver hot enough to melt. When the silver is liquid and the surface is constantly moving it is ready to pour into your mould. Keep the heat on the silver as you carefully pour it into the mould. Now you just have to wait and let it cool.
Ta Da! Once its cool just remove your piece and pop it in the pickle. The clay can be used again, just remove the black bits and keep the rest. When your piece is finished pickling simply remove the sprue and give it your desired finish. I like a high shine finish on most of my work so I usually use my pendant motor to sand and buff up my pieces.
Troubleshooting: If your mould only half filled with silver it could be that the channel you made to pour it in wasn’t big enough or was too deep. It could also be that the silver wasn’t hot enough when you poured it into the mould.
If your having trouble getting your object out of the mould you could try adding talcum powder before and after you press your piece into the clay. If the piece you want to cast has indentations/holes you can try adding a bit of clingfilm to your piece so the clay doesn’t get stuck in it.
Right well I hope I’ve been of some help, bit of a long blog this week, next time I promise it will be shorter and less technical! 🙂