Delft casting is a fine sand casting process, where jewellers create intricate designs by pouring molten metal into clay molds. This produces detailed shapes and patterns, resulting in rustic pieces that can then be refined and polished.
It’s a great way to cast pieces with very little cost and very little equipment. It’s a firm favourite of mine and is very rewarding when it works. Those of you who attended the casting course at The Brewery Arts Centre will know how tricky it can be and it really is a case of practicing to get your success rate up.
Basic Process
Break up clay
Pack bottom ring upside down
Press your master into the clay and dust with release powder
Place second ring on, lining up the marks
Pack the rest of the clay
Remove master and create pour hole and air vents
Put back together matching up marks again
Pour your molten silver and wait a bit
Open the mould and remove your cast piece
Casting can be a bit hit-and-miss some days. Here we see that the silver hasn’t flowed to the wings.
Key things I learned using the Delft Casting Technique:
Chop the clay up well to loosen it all before adding it to the mould rings.
Compact the delft clay firmly in the mould so that it takes a good impression but not so much that becomes hard to press in your source piece or master.
Don’t forget your release powder in between the two layers. An easy one to forget. Talc use commonly used but you can use flour too.
Sculpt the pour hole and think of water flowing. Make holes bigger, shape the pouring funnel nicely. Reduce all areas of friction that might slow the silver down as it enters the hollow within the mould.
The exact position of the pour hole is a bit of experimentation.
Your vent holes become more intuitive with experience. Add one to all points furthest away from the pour hole – on all deadends. Any unvented deadends may block the flow of silver and you’ll have to start over again.
It’s not uncommon to have silver come up your vent holes.
Make sure your ring marks on either side of the mould line up!
It takes longer than you think. Be patient and methodical.
Your success rate improves with practice but some pours will just fail. If they do, start again and try enlarging the pour hole and improving vents.
Get the molten silver poured as quickly as possible. From the moment it leaves the crucible, it is cooling.
Practice your pour as a dry run, much like a golfer practices before taking the shot. It can highlight an awkward wrist angle or obstacle. A slow-and-smooth movement is better.
Always be safe about it. At these temperatures, any accident will happen in milliseconds. Keep some water nearby in case you drop something hot.
If two or more pours fail, you may not have enough material, add more gold or silver and try again.
For release powder, use talc or even flour.
The result of a delft casting pour
The delft casting process in pictures
Andrew Berry, from At The Bench, has a wonderful series on the Delft casting technique:
Remember, when using Delft casting, it is better to have a little more material on the final cast piece of jewellery as it’s easier to remove silver than put it back on if too thin in places.
