One of the beauty's of Precious Metal Clay is it ability to create small piece quickly, and rather using a kiln for just one piece many designers prefer to use a hand torch to fire & start the sintering process.
Is the piece suitable for hand torch firing?
When deciding how to fire a piece consider its weight. Pieces weighing 25g or less are ideal of for torch firing, but also consider that your piece should be of a relatively even thickness for torch firing to work effectively. If your piece is of complex nature kiln firing is recommended to ensure even heat distribution.
Preparation before firing
Before starting to fire its worth considering the preparation of your working area. Make sure that you work in a well ventilated room, and that you have a dedicated area for soldering. Ensure that you have a heat proof surface i. e. soldering sheet, and then place a soldering block on top to work on. Plus consider you own safety with glasses, apron and tweezers and even protective gloves on hard to protect you whilst working.
The first time you torch fire clay, practice on a small piece to watch how the clay reacts to the heat, and to practice the firing process.
Preparation of the clay
Before you fire ensure you are happy with the shape and detail of your piece and that the piece is complete dry, as excess moisture will turn into steam causing the clay to expand or crack. If your piece contains gemstone, shells, or even findings consider how this will react to direct heat.
Firing the PMC
Once ignited adjust the torch flame so the flame is around 6cm, and the blue inner flame is around 4cm. Hold the torch at 45 degree, about 5cm away from the piece using the outer flame first to warm and then bring closer to increase the heat, ensure you keep the torch moving keeping the flame on the piece.
First the binder will begin to smoke and then flame, burning away. The clay will be then exposed and begin to glow red/orange (at sintering temperature). At this point continue firing the piece for 2-4 minutes depending on its size, be careful not to over fire the piece -if the piece beings to look shiny (indicating the surface is starting to melt) then move the torch away to reduce the heat. Once heated the particles fuse together and form a solid dense metal, and PMC3 only shrinks around 6% of its original size. To complete the process let the piece cool down to room temperature. Once fired silver PMC 3 becomes fine i. e. 99.9% pure - and can be hallmarked as fine silver.
Adam Hunter - E-commerce Marketing Manager of cooksongold.com. Cookson Precious Metals offer a choice of supplies from over 10,000 products including jewellery tools , findings, precious metal clay, wire and precious metal sheet - gold, silver, platinum and palladium plus technical information for jewellers, jobbers, designer, craftsmen, artisans and students.