What is the lost wax casting process?

One of the oldest methods of jewellery making around, lost wax casting dates back to the 3^rd century BC. Having been lost and rediscovered many times throughout history, the lost wax casting process is still used today for casting metal alloys. Keep on reading to find out what the lost wax process is and how you can use it for jewellery making.

What is lost wax casting?

Lost wax casting, also known as cire perdure, is an ancient process where metal alloys are made into a design from a wax mould. Throughout the years, the lost wax casting process hasn’t just been used for jewellery, it was also used to make sculptures and ornaments. Also, one of the main advantages to lost wax casting is the fact that you can replicate the same model as many times as you’d like. The most common metals used for this process are silver, gold, brass and bronze – so there are lots of opportunities for your jewellery making projects!

What is the lost wax casting process for jewellery? Step-by-step

Interested in giving it a go yourself? Follow our lost wax casting process steps below to find out how (using a silver ring as an example):

1. Using a wax tube, cut out the shape of a standard ring. Then, outline the pattern on the ring with a scribe, to provide a guidance on where the first cuts are going to be. 
2. Next, file the wax to the shape you require using a special carving file. Top tip: remember that you can file the wax down quite thin as silver weighs 11 times more than wax. 
3. Once the wax has been filed to your requirements, it’s time to attach a wax sprue to the ring. To do so, hold the sprue over a low flame until it starts to drip and then quickly place it on the ring in the heaviest area. 
4. Weigh the ring and make a note of how much it weighs. In order to calculate the amount of silver you need, consult these equations: for silver – calculate the weight of the wax multiplied by 11 and plus 10g to accommodate for the weight of the sprue.
5. After calculating how much silver is needed, fix the ring and the sprue to bottom of the flask – with a gap of at least 5mm between the edges and the top of the flask and the ring. 

Now you’ve completed the first few steps in the lost wax casting technique, you’re ready to move onto the next step in the process – the investment. Follow these instructions to find out what to do next:

1. Make sure the flask is attached to its rubber base and that the ring and sprue are securely attached. Then, fill the flask with water until approximately 5mm from the top. Once done, pour the water into a rubber bowl.
2. Next, weigh up the amount of investment powder you think you’ll need and sprinkle a tablespoon of it over the water. Remember, it will sink to the bottom to begin with, then will rise to the top once the correct amount of powder has been added. 
3. Once the powder has floated to the top of the bowl, mix for about 10 minutes to ensure the removal of air bubbles – any longer and the mixture will become too thick to work with. 
4. After you’ve given the mixture a good stir, put the rubber bowl on a vibrating plate. Keep a firm hold of the bowl and let as many air bubbles rise to the surface as you can. Then, squeeze the sides of the bowl as you pour the mixture into the flask. 
5. For roughly a minute or so, place the flask on the vibrating table to let any trapped air rise to the surface during the pouring to surface. 
6. Leave the flask to dry overnight – then peel away the rubber base where you fill find the wax sprue. 
7. With the sprue at the bottom, place the flask in the kiln to allow the melted wax to get out. Set the kiln between 150 and 200°C and leave for an hour. After the hour has passed, turn the heat up to 400°C for an hour and 30 minutes. To finish, increase the temperature to 720°C and hold for another hour – the varying temperatures ensure that the investment is fully dry and hardened, and the wax is thoroughly melted.

And now for the final stage in the process, the centrifugal casting. Carry out these steps to complete the lost wax casting process:

1. Put the required amount of silver in the crucible, remove any existing solder and cut any pieces of scrap so they all fit comfortably. Grab a pinch of powdered flux then sprinkle over the top. To compensate for the sprue, add an additional 10g of silver. 
2. Once you’ve put on your protective gloves, take the flask out from the kiln with a pair of large steel tongs. Then put it in the centrifugal machine and make sure that the crucible is closed up and is totally secured to the sprue end of the flask. 
3. Now everything is balanced and fastened tightly, allow for the metal to become molten and prepare the machine in the meantime. 
4. Check for any small lumps in the metal. If there aren’t any, you’re ready to activate the machine. Just make sure that there are no obstacles in the way of the centrifugal arm to avoid it from stalling. 
5. Once the machine has stopped spinning and the bottom of the flask has turned from red to black, remove it with tongs and submerge in a metal bucket of cold water. Move the flask from side to side until the investment disperses and the metal casting is revealed. 
6. Lastly, pickle and scrub the casting to get rid of any residual investment, then remove all of the sprues with a jeweller’s saw. To finish off, file and polish the ring – then you can choose to keep it as a unique piece or send away for a rubber mould so that it can be replicated. 

And that’s it! You’ll be asking ‘what is the lost wax casting process’ no more. Ready to try it yourself? Make sure you have all the wax working equipment and casting pieces you need before you start. 

source https://www.cooksongold.com/blog/learn/what-is-the-lost-wax-casting-process/