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Frequently Asked Questions About PMC
Here are some of the questions we hear most often. For more questions (and answers), visit the Getting Started section of www.PMCguild.com. You can also search for specific terms using the Search feature at that site.
Q: Is PMC hallmark quality?
A: Yes, you can have PMC hallmarked by the Assay office, where it will be stamped 999. This refers to the proportion of silver in parts per thousand. Sterling is stamped 925 because there are nine hundred and twenty five parts of silver per thousand parts. The remaining seventy-five parts are usually copper
The normal process of hallmarking involves a small amount of metal being scraped off and tested. Several punches are then used to mark the item including the purity, the makers mark, the year and which city the mark was struck in.
Some PMC artists prefer to have their items laser hallmarked which doesn't involve striking a physical blow and therefore potentially poses less damage to the item. Instead, the laser etches away the same marks without the need for a hammer blow.
To have items Hallmarked you must first register with the Assay Office. There are offices in London, Birmingham, Sheffield, and Edinburgh and they each have a different symbol as their mark. It is not required that you register with your nearest office, so you can choose the emblem you like best. You will find more information at www.thegoldsmiths.co.uk
In the UK, you are not legally required to hallmark silver items weighing less than 7.5 grams but most galleries will only take your work if it is hallmarked. This shows a level of commitment to your work and also means the Gallery can sell the item with confidence. If you are selling items at craft shows as silver and they weigh over 7.5 grams you are required by law to have them hallmarked.
Q: Can I treat PMC just like sterling after it is fired?
A: Mostly. You can polish, file, bend, drill and solder PMC. You need to remember that PMC is fine silver, while sterling is an alloy of silver and copper. Fine silver is a little softer and doesn't work harden in the same way as Sterling. Your PMC is strongest if fired in a kiln, so if you intend to bend the piece after firing (like forming into a ring shape) it is best to use a kiln. Torch firing is perfectly adequate for most items though.
Q: Why is PMC so expensive?
A: Because is it a high tech material, PMC costs more than conventional silver wire and sheet. The cost is balanced by the amazing speed with which forms can be made, and the very low investment in tools. Also, all versions of PMC can be rehydrated before firing, so there is no waste.
Q: I solder sterling to PMC?
A: Yes but don't use Hard solder because the melting point of hard is too close to the melting point of the PMC. Instead, use Medium or Easy solder. It is not necessary to flux the PMC because it is pure silver but you will need to flux the sterling in the area you wish to solder. This prevents oxidisation and helps the solder to flow.
Because of microscopic spaces, fired PMC soaks up solder more than sterling. To minimize this, I recommend burnishing the area of PMC where the solder will be. This helps to compact the surface so the PMC is less porous. I usually melt the solder into a ball on my piece of sterling, and then heat the piece of PMC until it gets an orange glow. This is the melting point of the solder, so then I bring the piece of solder-topped sterling into contact with the hot PMC. At the moment the solder starts to flow between the two pieces, I stop heating and hold still, allowing the solder to resolidify.
Q: Can I add sterling silver to my PMC pieces?
A: You can add sterling while you are creating your PMC piece but you will need to use PMC3 and fire at under 700 degrees C. This is because at higher temperatures, the crystalline structure of sterling becomes brittle and wrinkly on the surface (this is known as reticulation). You can also add sterling silver fittings like earring hooks or jump rings after your PMC piece is finished.
Q: My PMC looks white after I fired it. What did I do wrong?
A: White is the natural colour of the newly fired PMC. The PMC remains white until you polish or affect the surface in some way.
Q: What if I don't have a tumble polisher?
A: There are many ways of polishing PMC without a tumbler. You can get a nice soft sheen by rubbing the fired piece with pumice paste or with a brass bristle brush and soapy water. You can highlight certain areas by rubbing with a burnisher (a smooth piece of steel) or fine emery papers. You can achieve a higher shine with polishing mops on a polishing motor or in a small hand-held motor like a Dremmel.
Q: I have an enamelling kiln with no pyrometer. Can I use that to fire my PMC?
A: This is tricky because you won't know when the kiln has reached the correct firing temperature. There is a danger you might melt the PMC piece if the kiln gets too hot. The other end of the problem is that the PMC might not get hot enough to sinter properly. You might be able to get a pyrometer fitted to the kiln and you should consult a specialist to do this for you. Don't forget you can also fire PMC+ and PMC3 with a small hand-held gas torch.
Q: Does PMC have a shelf life and what is the best way to store opened packets?
A: PMC has an indefinite shelf life, but over time the moisture in the mix will evaporate. You can store opened packets in cling film or plastic bags in a cool place.
Q: I found a PMC packet I opened a while ago and it is a hard lump. What can I do?
A: All is not lost! Even a hard lump can be returned to a clay-like state. PMC only has 3 ingredients; fine silver particles, binder, and water. All that has happened here is that the water has evaporated so we need to put the water back again.
Shave pieces off the hard lump with a craft knife onto a piece of cling film. Keep going until the whole lump is chopped up into little pieces. Spray the chopped pieces with water and close the cling film up airtight. Time is your friend here — set the packet aside for a day or two to allow the water to seep into the lump. You can gently work the water into the dried PMC pieces with your fingers outside of the cling film. It takes a little practice to judge how much water to add but if you overdo it and the clay becomes too slimy you can simply leave it open to the air to dry out a little. Up until the point when your PMC piece is heated, it can always be salvaged and returned to a workable clay texture.
Q: Which stones can I fire in place?
A: There are quite a few stones that can withstand the lower firing temperatures for PMC3 but you should use caution because most stones don't like to be heated or cooled down quickly. You can download a gemstone test list here.
www.pmcguild.com/download/Tech_Data/Firing_Gemstones_Chart.pdf
Q: My piece broke after I fired it. Can I mend it with more PMC?
A: Yes. When adding fresh PMC to bond with metal that is already hard, you should extend the firing time to at least double the normal schedule. This allows the silver particles from one to penetrate into each other. Extend the time, but not the temperature. You can go up to 1650°F (900°C) safely, but no higher.
Q: I want to teach PMC classes. Is there a qualification I can take?
A: The best qualification is plenty of experience. Currently there isn't a degree or qualification course available. Many people learn by experimenting with the material. There are several books and many videotapes available that will provide the information you need. In fact on this very website you'll find short video clips, a free instruction booklet, and lots of tips. Of course no amount of printed information can take the place of the interaction with a good teacher and the stimulating environment of a classroom or workshop.
Q: Do I have to be certified to teach?
A: No, anyone who feels qualified can teach a class. There is no formal requirement to offer a class, but you are able to take a certification class if you want to. People interested in teaching should read the short list of questions and answers designed specifically for them at "About Teaching PMC...."