Firing
Firing Precious Metal Clay (PMC)
Firing is one of the most important aspects of working with Precious Metal Clay (PMC). As PMC is made up almost entirely of pure silver particles items can be polished even though they have not been fired. The only way you will find out is when the piece breaks whilst it is being worn.
PMC will always look white once fired as this is its natural state. By polishing ie, smoothing the surface the PMC will gain its silver colour. The more you polish the brighter the silver will look.
TORCH FIRING
Pieces the size and thickness of a 50 pence piece can be torch fired. Gently heat the piece, wait for the binder to burn off and the piece to glow a pale orange. Once the piece glows orange, continue for a minimum of two minutes and keep the whole piece heated evenly. If your piece starts to look silver on the surface you are in danger of melting your silver. Pull the torch up.
Once fired, quench in a cup of water to strengthen the metal. Please note, this applies to items that are made of PMC ONLY. Items containing gemstones, glass or ceramics need to be left to cool.
Items that can be torch fired should be no larger or thicker than a 50 pence piece.It may contain fireproof gemstones.
KILN FIRING
We no longer sell kilns but recommend trying to find a secondhand Evenheat Kiln or Paragon SC2. Take a look at our Youtube clip buying a kiln.
When buying a kiln it is important that you buy one that is safe to use and fires to the temperature states on the control panel.
Items that need to be fired in a kiln are items:
- larger or thicker than a 50 pence piece
- 3D objects e.g. box shapes
- contain natural gemstones
- contain glass
- contain ceramics
- contain natural materials e.g. pods, leaves and paper
Optimum Kiln Firing Temperatures and Times for strength vs minimal shrinkage
PMC Flex and PMC3: Fire at 800C for 30 minutes. Make your rings 3 US sizes larger to allow for shrinkage.
PMC Flex and PMC3 including low fire items such as glass, ceramics and natural gemstones: Fire at 600C for 45 minutes. Make your rings 2 US sizes larger to allow for shrinkage.
PMC Onefire Sterling: 900C for one hour
Original PMC Sterling: This is a 2 part firing process. 1st Fire: 540C for 30 mins on an open shelf. 2nd Firing: 820C for 90 Mins in carbon.
Torch Firing PMC3, PMC Flex, PMC+ and 22K Gold
Pieces the size and thickness of a 50p piece can be fired with a butane gas torch. Place the item on a torch block. Gently heat the piece, wait for the binder to burn off and the piece to glow a pale orange. Once it is glowing time for a minimum of 2 minutes (5mins for PMC+, 7mins for 22K gold), keeping the whole piece heated throughout.
Once fired, PMC can be hallmarked as Fine Silver (.999) or Sterling Silver (.925) at any of the independent UK Assay Offices.
Birmingham Assay Office http://www.theassayoffice.co.uk
Edinburgh Assay Office: http://www.edinburghassayoffice.co.uk
London Assay Office: http://www.thegoldsmiths.co.uk/welcome-to-the-assay-office
Sheffield Assay Office: http://www.assayoffice.co.uk
Please note items of silver weighing less than 7.78g and items of gold weighing less than 1g are exempt from hallmarking. This means they can legally be sold without being hallmarked. The silver/gold weight on the packs of will help you calculate the weight of your fired pieces.
