fusion journal of the pmc guild The Journal of the International PMC Guild PMC Pro tm 14 bracelet 2010 /4 barbara becker simon fusion fourteen Jeanette Landenwitch, Bracelet, 900 silver, 24k gold Last July, representatives of Mitsubishi Materials announced a new kind of clay they are calling PMC Pro™. Last month the new form of precious metal clay became available for purchase in the US and is currently sold by many of the companies that sell fine silver PMC and base metal clays. In this issue of Fusion, we will do our best to provide practical information about the newest member of the PMC family. What is it? PMC Pro™ is an alloy of silver and copper in the proportion of nine to one. That is, 10% is copper and 90% is silver. As with other clays, the only other ingredients are nonmetals (water and binder) that burn away in the process of converting the clay to solid metal. How is it used? PMC Pro™ is gray in color but other than that it behaves in ways very similar to fine silver clays. Or perhaps better. It can be sculpted, rolled, molded, and carved. Artists who have worked with it report that PMC Pro™ has a longer working time and better green strength than even their favorite fine silver clay. It can be rolled into sheets and rods, stretched, squeezed, reconditioned, and in every way treated like the other clays. To make slip with PMC Pro™, either press water into a bit of the clay or mix page 2 journal of the pmc guild PMCguild International The PMC Guild is a members organization with the mission of providing support, education, and exposure for artists working in Precious Metal Clay. PMC Guild 1921 Cliffview Lane Florence, KY 41042 Executive Director Tim McCreight, knife, 900 silver, 4 inches Jeanette Landenwitch [email protected] water with filings and carving scraps. Early tests indi- Treasurer cate that adding an essential oil such as lavender oil Darnall Burks to slip increases the strength of a joint when bonding [email protected] previously fired parts. Communications At the workbench, PMC Pro™ requires very little Tim McCreight special attention. In most cases it is possible to use [email protected] the same tools, the exceptions being sandpaper and Journal Editor similar polishing materials what cannot be completely Bob Keyes cleansed of powders. For rollers, molds, blades, and [email protected] brushes, simple cleaning when moving from one kind of clay to another is sufficient. Scraps of PMC Pro™ Chapter Liaison should not be combined with scraps of fine silver clays. Jobie McCreight Fagans [email protected] Drying is similar to fine silver clays and at this point work can be in proximity. For example, there Web Manager is no problem in having pieces of PMC Pro™ in a Sadelle Wiltshire dehydrator alongside pieces made of fine silver clay. As [email protected] with all clays, allow sufficient time to ensure that the clay is dry all the way through. Thicker pieces require longer drying time. To Join, Renew, or Edit Info Online How is it fired? www.PMCguild.com Because of the copper content, PMC Pro™ must be fired in a reducing atmosphere. This is done by cover- Membership Questions (toll-free) ing work under about a half inch of activated carbon, 866–315–6487 usually contained in a stainless steel vessel. Assuming page 3 Speak with the Director 859–586–0595 fusion fourteen Celie Fago Three Rings, 900 silver, 24k gold Square Bos, 900 silver, 2 inches high the work is properly dry, the ramping, or rate at which the kiln heats up, can be fast. Bring the work to 1400° F (760° C) and hold there for at least one hour. For larger pieces or when many pieces are being fired in one vessel, the manufacturer recommends extending the time to two hours. Technically work can be removed from carbon as soon as the firing is completed but this is not recommended for two reasons. Handling a hot pan filled with glowing carbon is dangerous, and exposing the work when hot will create a gray oxide film on the metal. If possible, allow the work and vessel to cool to no more than a couple hundred degrees before removing the work. Experiments have also been done with a two-step or double-fire program in which work is fired first in air and then in carbon. This is required when making work that includes elements made from fine silver clay alongside elements made from PMC Pro™. When dry, set work on a firing shelf and heat it to 1000° F (538° C) for 30 minutes. Allow to cool until the work can be safely moved, then transfer it to a pan and see that it is surrounded by about a half inch of carbon. Heat to 1400° F and hold for at least a half hour. Some people prefer to use this two-step firing schedule for PMC Pro™ even when fine silver clays are not involved. Finishing PMC Pro™ can be filed, sanded, patinaed, and polished just like other versions of PMC. As mentioned, use separate polishing equipment to avoid contamination, but otherwise follow the same methods normally used. PMC Pro™ will achieve a pleasant silver glow when finished with a page 4 journal of the pmc guild Hattie Sanderson, Necklace, 900 silver, beads soapy brass brush. To create a highly reflective shine, use polishing papers or a machine buff with tripoli, White Diamond, or similar compounds. Can PMC Pro™ be soldered? As shown in the tables that follow, the melting point of fired PMC Pro™ is around 1475F (800 C). This tells us that we must be careful not to heat above 1450. This means that hard silver solder is not recommended for PMC Pro™, but easy or medium solder will be fine. Use any convenient silver brazing flux. It is also possible Barbara Becker Simon, Rings, to join pieces with low temperature 900 silver, solders like TIX or Sta-Bright. page 5 fusion fourteen Comparisons of Some Metal Clays The chart below provides some statistical comparison between Original PMC, PMC3, and PMC Pro™. The bottom four rows show dramatically how much stronger the alloy material is than its pure metal siblings. The tensile strength, measured in Newtons per square millimeter, is more than twice as great as PMC3 and almost four times greater than Original PMC. The figure for PMC Pro™ translates to about 30,000 pounds per square inch. To put this into jewelry-related terms, PMC Pro™ is less likely to stretch, much less likely to bend out of shape, and will stand up to abra- sion twice as well as even the densest fine silver clay. This is not a factor of firing, per se, but the result of the alloying process. Here is an example: copper and zinc are both soft metals but when they are combined the yield brass, which is much tougher than either ingredient. The same phenom- enon is at work here. original PMC PMC PMC 3 Pro ™ Metal Fine silver Fine silver 90% silver alloy Metal Content 77% clay weight 90% clay weight 90% clay weight Shrinkage (size) 25–30% 10–15% 15–20% Recommended 1400˚F in carbon 1650˚F /120 min. 1650˚F /30 min Firing for 60 minutes Elongation 15% 35% 30% 2 Tensile Strength 60 N/mm 140 N/mm2 210 N/mm2 2 Bending Strength 30 N/mm 30 N/mm2 150 N/mm2 Surface Hardness n/a ( Vickers) 30 HV 60 HV Density 7.9 g/cm3 9.7 g/cm3 9.7 g/cm3 page 6 journal of the pmc guild Shrinkage Tests As with all forms of metal clay, the recipe calls for metal powder, water, and a binder. Because the water and binder are driven off or burned up during firing, the resulting object will be smaller than it was before. Because the water and binder are perfectly distributed in the clay, the shrinkage will be proportionate. As the miniscule bits of powder fuse to- gether, they merge and take up less room, adding to the rate of shrinkage (again proportionately). Because of this, extending firing time will usually result in slightly more reduction in size.What this shows us is that PMC Pro™ shrinks more than PMC3 but not quite as much as Original PMC. The rate is described as 15-20%. 28.8 mm Original PMC 32.8 mm PMC Pro™ 35 mm PMC3 40 mm The first step in the experiment is to make bars of a fixed size, here 40 mm. Activated Carbon Carbon is often used for filters because it combines easily with oxygen and many other things. As with a sponge, the greater the surface area, the more active this absorption becomes and that is why we use “acti- vated” carbon. Note the great amount of surface area in this photomicrograph. Activated carbon at 1500 x. Photo by Microangela page 7 fusion fourteen Special Case: Combining Metal Clays First, let’s be clear on the difference between combining and joining PMC Pro™ with fine silver clays. Because of their different firing requirements, the manufacturer advises against physically mixing PMC Pro with any other metal clay. That said, some designs will invite different clays for dif- ferent reasons. Imagine a necklace clasp in which a cap that will connect with a strand is made of PMC+ while the hook and eye is made of PMC Pro™ for strength. Or again, a ring in which a thick top portion is made of PMC3 while a delicate shank uses PMC Pro™, again because of its greater strength.