Firing Silver Clay – Part 1
One of the things I am asked most by my students is firing silver clay. How long should it be fired for? What are the rules about firing with stones in place? Is it better to fire with a kiln? If you too are looking for the answers to these questions then this series of blogs will hopefully provide them and put a few fears to bed at the same time!
Generally there are two main ways to fire your silver clay, by hand and by kiln. There are rules that you should follow if you want to get a fully sintered piece and there are things you should know if you want the strongest piece possible.
The process of firing silver clay
Whether you fire by hand or by kiln, the process that the clay goes through to change into metal is the same. If you’ve never fired before, then some of it may take you by surprise!
So what are the steps for firing?
- When you apply heat to your piece, it will begin to produce smoke.
- Then it will produce a flame. This is the organic binder which held the clay together, burning away. The size of the flame depends on the size of the piece you are firing. The larger the piece, the more flame it will produce. Be careful at this stage if you are firing by hand, because sometimes the flame can react with the torch and put your torch flame out. Don’t panic! Just continue and reignite your torch.
- Your piece will start to heat up until it reaches a lovely warm orange/peachy glow. It will turn white and you may see it shrinking. The orange / peachy stage is called ‘SINTERING’ and this is very important, because this is when all the silver particles begin to join together.
- If your piece is large or thin it may curl up as it shrinks, but don’t worry it will return to the shape it started out by the time the firing is complete.
Instructions for hand firing silver clay with a torch
Most silver clays can be hand-fired with a butane torch; certainly the most recent versions of both Mitsubishi’s (PMC3) and Aida’s (ACS) were designed with hand-firing in mind.
- A good quality butane torch, preferably with an ignition button that does not require to be pushed throughout the firing and a stand.
- A firing block. It is also advisable to place your firing block on something else to protect your surface underneath. I use a granite block bought very cheaply from a local supermarket. A house brick is also a good and inexpensive alternative.
If you are ‘quenching’ your work – i.e. dowsing in water after firing (this is NOT advisable if the piece has stones embedded), you will also need;
- A pair of tweezers
- A bowl of water
Follow these easy instructions and you will have a beautifully handfired piece in no time.
- Place the item to be fired on your firing block.
- Ignite the torch in the normal manner and hold over your piece, keeping a distance of about 20cm. Make sure you have a blue flame from the torch; a yellow soft flame will not produce the heat necessary to achieve the required temperature.
- In slow, deliberate circular movements, keep the heat on the piece. You should see smoke within about 10 seconds. If you do not, move your torch in closer.
- Once you see smoke, then the flame will not be far behind. Do not worry about the flame from the piece, that’s the binder burning away and it should only last for a few seconds.
- Keep the torch on the piece and keep moving in a slow circular motion, at this point you are ramping the temperature up to the sintering point. You may see the piece turning white and shrinking, this is normal. You may also witness the piece curling up at the edges but again this is normal and temporary, the piece will return to its pre-fired shape after firing.
- Just prior to the silver reaching the optimum temperature, you may see a ‘halo’ around your piece which indicates it is nearing the correct temperature. Keep the slow deliberate movement with the torch until your piece turns the peachy orange colour.
- This is when you start your timer. Your piece should be fired for a MINIMUM of two minutes. If your piece starts to get hotter – i.e. the colour changes from that peachy orange to a deeper orange bordering on red, then move your torch up a few centimetres to let it cool down. Do not move the torch away completely, you still need to maintain a constant temperature for two minutes.
- Once the time is up, pick up with piece with your tweezers and drop into the bowl of water. Wait until you hear a whooshing, popping sound and then it’s safe to pick up.
Dos and Don’ts when hand firing silver clay
Here are some dos and don’ts to bear in mind when hand-firing silver clay.
- Do make sure you start the timer as soon as the piece turns the peachy orange colour
- Do fire for longer than the 2 minute minimum if you can – the longer you fire, the stronger your piece.
- Do make sure you have all the equipment to hand before beginning firing
- Don’t quench anything that has a stone in it
- Don’t hand fire the following;
- Anything with glass in it – the glass is likely to shatter with the direct heat from a torch
- Any hollow object which has been formed round a combustible material such as wood or cork clay
- Do support any fragile item or shaped item with vermiculite or kiln blanket to prevent it slumping during firing.
- Do make sure your piece is 100% dry before firing. If it’s not, the water particles inside the clay will expand and pop causing disfiguration on your piece.
- Do remember that PMC+ needs a long time to sinter when hand-firing. Fire PMC+ by hand for a minimum of 10 minutes.
- Do remember that sterling silver PMC CANNOT be hand-fired