At the PMC Guild Conference last week, two new metal clay products were announced.

Metal Adventures Quick Fire Bronze was released and sample packages were distributed to conference attendees.  I haven’t tried mine yet, but it should be another advance in the base metal clay toolkit.
Mitsubishi announced and demonstrated their PMC PRO, but it won’t be available until October.  After Firing it is 90% silver and 10% undisclosed metals.  They will tell us about the other metals in October when it is released.  I have the impression they are holding back until all the patents & etc. are properly filed.  It is stronger than the fine silver metal clays, but at only 90% silver cannot be hallmarked as sterling (92.5% silver).  They are suggesting a 1 hour firing in carbon.  It looks promising for rings and pieces that need more strength, but the lower than sterling content may make it a harder sell.

If you can’t wait for PMC Pro to come out, you can experiment with making your own Sterling  or Shibuichi alloys, you can read about them in my article on Married Metal Clays

by Mary Ellin D’Agostino

Where there is fire…

…there are smoke and fumes. Plus, we have to deal with dust from metal clays, enamels, and other materials we work with in our studios.  This is the first installment in a series on the health and safety issues metal clay artists need to consider.

While the binders in silver clay are non-toxic, fumes and particulates from firing are not great to breathe.  Smoke from metal clays is similar to those you get when burning food.  Those are not great to breathe either, but not necessarily something to cause panic (unless the burning goes too far and your house catches on fire!).  You can read reports on organic gasses released during firing on the PMC Guild website.  The Manufacturers’ Data Safety Sheets (MSDS) for PMC Silver and Art Clay Silver may also be useful.  All confirm the non-toxic nature of silver clay binders.

All of them also say to have “adequate ventilation” when firing.  So just what is adequate ventilation?  Linda Kaye-Moses believes that we should be thinking “active” rather than just “adequate” ventilation. An open window and/or doorway make a good start, but not usually enough for even “adequate” where toxic fumes are involved. A fan that blows air from an open window or door toward another open window creating a cross breeze and flow of fresh air is a lot better for general room ventilation.  However, if your work creates a localized source of dust or fumes, a fume hood or filtration system that will suck away the contaminated air is a good idea.  Such a system may also be required in cases where there are not multiple windows and doors that can be opened or when weather makes open windows not an option.  Excellent discussions and advice can be found on the Ganoksin jeweler’s forum by doing a search on “ventilation,” “workshop safety,” or scanning their archives.  Two excellent places to start are Charles Lewton Brain’s articles on Basic Safety Principles, Ventilation in Your Jewelry Workshop,   Jewelry Workshop Safety Report, and Brandney W. Simon’s  Workshop Air Quality.  When you read these articles, you will find links to paid advertisements selling ventilation equipment. There are is a whole lot more on the Ganoksin archives, including discussions and directions for building your own fume hood.  Ganoksin and its Orchid discussion forum is the best resource for jewelers on the web.

If the only concern is dust rather than fumes, a true HEPA air filter of the type sold for home allergy sufferers may be sufficient for your needs.   These can be placed in front of your work area to suck up any airborne dust down to 4 microns in size.  I use HEPA air filters originally purchased for my house-dust allergy.  These are an economical solution for the hobbyist and small scale artisan who is not working with materials that produce fumes.  High production studios, may want to investigate further and purchase filters designed for industrial use.  No matter what type of filter you have, be sure to change the carbon pre- and HEPA filters regularly.  For studio use, you may have to replace them more frequently than for standard household use.

If the concern is also fumes from the materials being used (resins, soldering, firing, & etc.), you should have a filtration system or fume hood that pulls both dust and fumes away and either filters them before returning the air to the room or vents to the outdoors.  Brands include HAKKO, Sentry Air Systems, Electrocorp, Vaniman, Lab-Air, and others—I know, I should include links here, but I am lazy and these names give you a place to start an internet search.  Some of these units are portable and have hoses that can be positioned to focus on your work area.

Further Reading:

The US EPA has an excellent  page with information on comparing the various air purifying technologies and a guide to issues in indoor air quality.  I know the government info is far from perfect, but these sites are great places to start lo0king for reliable information before moving on to the industry, muck-raking, and alarmist sites that pepper the internet.

Coming Soon:
Dust, Fumes, Smoke, and Fire: Part 2:

A discussion of the health and safety risks surrounding the powdered silver, gold, copper, and bronze used in metal clays.

© 2010 Mary Ellin D’Agostino

By Mary Ellin D’Agostino

I have known for some time that one can revitalize old dried or partially dried cork clay by adding wanter, letting it sit, and kneading relentlessly.  But now that wood clays have supplanted cork clay, many of us want to know how to rejuvenate the wood clays.  Since wood clay made an entrance, there have been two brands used and sold by metal clay suppliers.  The first was a Japanese brand that came in packages of similar size to the cork clay (about 8 oz).   The most commonly sold current brand is from Spain and is called Patwood by Jovi®.

Neither of the wood clays could be successfully rejuvenated by adding water.  In fact, I had been having trouble with the Jovi brand sticking to itself even if it was just a little dried out.  Adding water did not seem to help.  Glycerine didn’t seem to help.  Then my friend and colleague Judy Pagnusat said she had tried adding common school glue.  That did the trick.  She used the Elmer’s® blue school glue.  I tried white glue and found the same thing.  I also tried rehydrating some completely dried Patwood and found that by adding water, letting it sit for a while, adding glue, and kneading, it came back to its original pliable form.

So, to rejuvenate wood clay, when it gets annoying, just knead in common white glue.  If it is really dry, add water and glue.  It is a messy process, but the results are worth it.

PS:  Thanks to Linda Kaye-Moses for the reminder:  Be sure to check out the ingredients and MSDS of the glue you use to make sure it is safe and will not produce hazardous compounds when burned.  Elmer’s Glue-All, School Glue, and their blue gel school glue are not particularly hazardous when burned (no hazardous polymerization and the decomposition compounds are CO and CO2), but you do need good ventilation, as you do anytime you burn something.

© 2010 Mary Ellin D’Agostino

By Mary Ellin D’Agostino

People often ask about what they need to fire their silver clay. Do they need a kiln?  Can they use their old ceramic or glass kiln? What kiln should they buy?

Let me say first that silver and gold clays do not care what your heat source is. Heat it long enough and hot enough and you will have a good result. Heat it too hot and it will melt. If it doesn’t get hot enough for a long enough time, it will be brittle. There are many firing options available and all have their pros and cons mostly having to do with expense, convenience, and consistency of use. In this article, I discuss several why or why not you might choose any particular firing method.

Base metal clays have additional issues to consider when firing.  These clays are still in their infancy and the most reliable firings methods are kiln based.  Many metal clay artists and manufacturers are working on coming up with reliable firing alternatives.

Hot Pot: The reason to purchase a Hot Pot is if you are a new user of silver clay, don’t know if you will continue using it, are concerned about using a torch (often this means you are concerned about the open flame or of the possibility of melting your piece), and only firing the low fire metal clays. Hot pots are a good choice for people who match one or more of these criteria. The Hot Pot, WHEN USED CORRECTLY, gives a perfectly adequate firing–I do not recommend it for firing rings or other items that need to be very strong unless the maker has no other firing options. These items should be fired in a kiln for a longer/hotter firing schedule than is recommended by the manufacturers. Even when firing such items with a torch, it is highly recommended that they be fired for longer than one might fire a pendant. The choice to fire twice is often made with a torch and kiln as well as the Hot Pot and reflects more on the particular piece and the person making it than on the type of firing system used. Finally, part of the concern over the Hot Pot may be due to people using the wrong fuel for it. When purchasing replacement fuel, it is important to buy the right kind. Not all gel fuels are the same! Unfortunately this means that the safest choice is to buy the Hot Pot branded fuel as the heating characteristics of gel fuels is not listed on the various brands found in hardware or camping stores. Hot pots are only for low fire silver clays (PMC3 or ArtClay650)!

Torch: That said, the torch is more versatile and I prefer it for that reason, but many people are concerned about using an open flame. A person using a torch to fire metal clay should be very clear on what is meant by “glowing orange” as many people have under-fired their pieces when their “glowing orange” is different than what experienced metalsmiths and torch fire-ers understand the term to mean. This is one of the biggest drawbacks to learning from books and instructional media. Nothing beats learning from a good experienced teacher in person.

Stove Top: A stove sop can be a good firing option if you actually have a gas stove. These are not as common as many people think. While gas is cheaper to run, it is a lot less expensive to install an electric stove and that is what many builders have chosen in the USA. In my experience, you can’t really just set it and forget it because you may need to adjust the flame while firing. Also, you need to be sure to use a stainless steel wire grid and not standard hardware cloth, which is usually galvanized and will deteriorate during firing. Camp stoves are far more problematic than the household range as the flame does not remain consistent–it changes as the level of fuel in the propane or butane canister goes down and as the canister becomes colder while firing. Hence the Speed Fire Cone™, which concentrates the heat AND comes with a pyrometer so you know what your temperature is. The SF cone needs to be monitored as well. Also, the most consistent result will be gained if using a large BBQ type tank for the butane/propane–an adaptor is needed in this case for the SF Cone.

Kiln: Kilns give the most consistent firing assuming one has a reliable pyrometer in the kiln. These are available in a wide range of options, but if one can afford it, a kiln with (or that can be retrofitted with) a digital controller and pyrometer is the way to go. The kilns designed for use with metal clay products–Evenheat (sierra) and Paragon–are the best for using with silver and gold clays because they are designed to have a very consistent temperature throughout the firing chamber.

Lots of people like the Ultralite™ kiln because of its small size and relatively low cost. It is comparable to the SF cone at its base price, but the special metal clay inserts may make it a little more costly. It does take longer to heat than the SF Cone, but does run on electric.

The easiest and most reliable method for firing any type of silver or gold clay is a small programmable kiln with a ceramic fiber or refractory brick muffle. A muffle is the insulating part of the kiln. Ceramic fiber is a good choice for silver and gold clays because of it is an excellent insulator, lightweight, and the heating elements for the kiln can be embedded in the sides. Traditional refractory brick insulation is bulky and kilns made from it tend to weigh a lot, take up a lot of space, and have the kiln heating exposed on the interior of the kiln. Ceramic fiber is a space age material that can be formed in a mold with the kiln elements in place. The embedded elements are not exposed so you can load, unload, and crash cool the kiln without worrying that the elements will be damaged. The exposed elements in a traditional kiln require periodic replacement because they can become damaged if the kiln is opened while hot or by glass, glazes, and other substances in the firing chamber. On the other hand, traditional brick kilns are a lot less expensive and the elements are inexpensive to replace when they wear out. If you plan on firing bronze and copper clays using the “bury it in carbon” long firing schedules, brick kilns with exposed elements are preferred because the long firing times wear out the elements more quickly and, if you do a lot of firing, you will appreciate their easy and inexpensive replacement. When the elements go in a ceramic fiber kiln, you have to replace the whole muffle, which is expensive.

The size of the kiln is an issue because the larger the kiln, the more difficult it is to have even heating throughout the firing chamber. By “small” I mean a kiln that has an interior chamber that has a footprint less than or equal to 12″ at it’s widest point; a little bigger will be ok, but the typical 18″-20″ kiln may give less even heating. A large ceramic kiln will have hot and cool spots which can make firing metal clays chancy. This is not to say that they can’t be used, but you should know your kiln well and place any silver or gold clay objects near the thermocouple or cones so that they are heated to the desired temperature.

Top loading and front loading kilns also have different heating characteristics. When firing bronze and copper clays in a carbon filled box, a top loading kiln is preferred because the box is heated on all sides. Front loading kilns do not usually have heating elements in the door and the side of the firing box facing the kiln door remains cooler than the rest of it.

Glass and silver clay kilns tend to have maximum operating temperatures of 2000°F/1093°C and extended firings at the hotter bronze/copper temperatures will wear out the kiln elements relatively quickly.  These kilns are designed to be fired at glass fusing and silver clay firing temperatures and will last for years when used for these purposes.  If you are doing the long carbon filled box firings for copper and bronze, you may want to look into using a kiln designed for firing ceramics.  These cost more because they are made using materials that are durable at the higher temperatures required for firing stoneware and porcelain.

Happy Firing!

Note:  I have left off links to products and brands in the text because I am being lazy.  However, I would like to note that PMC Connection, our sponsor, sells all of these devices except maybe  the kitchen range.

© 2010 Mary Ellin D’Agostino

by Mary Ellin D’Agostino

Some time ago, I ran some experiments to help one of my former students track down a problem.   She and some of her students experienced curling, warping, surface deformation, spots, and what they thought was incomplete sintering of the silver clay.  Was it a problem with the PMC she was using?  I asked her to come over and bring the problem clay so we could try to figure out what was going on.  On her way over, she had a light-bulb moment and realized that the work surfaces she was using might be made from aluminum.  That gave us an excellent place to start.

Most of us know that silver clays (PMC or ACS) can be contaminated by contact with aluminum, but many of us ask just what is the problem and how long must the contact be to contaminate the silver?

The essence of the problem arises from an electrolytic reaction between the silver and the aluminum (or aluminum oxide).  A full technical description is beyond me, but my understanding is that the reaction between the two is essentially the same as what happens in an alkaline battery.  What we are getting is similar to the corrosion/crud that forms on the battery contacts.

What I can give you is a description of what happens to the silver clay from a practical viewpoint.  The symptoms of aluminum contamination of PMC or ACS are:

  • Discoloration: Dark spots or areas of discoloration may appear on the unfired silver clay.  Discoloration might not appear until after firing your PMC/ACS.  After firing, discoloration can sometimes be polished away, but “ghost spots” will reappear later.
  • Warping: During firing, contaminated pieces may warp, curl, and deform dramatically.  This far exceeds the minor kinds of warping we sometimes see when firing normal silver clay jewelry.
  • Brittleness & Flaking: Pieces may be brittle and surface areas may flake or spaul off of the piece.  This can be confused with incomplete sintering of normal metal clay.  It is, in fact, due to an incomplete sintering because the contaminated metal clay is chemically changed and cannot sinter properly.

The Experiment

Going back to the original problem to test whether the problem was due to “bad clay” or had been contaminated by working it on aluminum surfaces, we tested the aluminum contamination theory by exposing silver clay from a single package to varying lengths of time in contact with aluminum. One package of PMC+ clay was broken into four pieces.  Each piece was rolled out into a slab 1mm thick and marked with a letters A-D and treated as follows:

A) The clay was worked on the aluminum and dried elsewhere,

B) worked and dried on the aluminum,

C) worked on plastic and dried on aluminum,  and

D) worked and dried on non-aluminum surfaces.

All the pieces were dried on a heating tray for about 15 minutes and then fired in a kiln at 1650°F for 10 minutes


The longer the silver clay is left on the aluminum, the worse the reaction.  The contamination caused dark spots and a brittle clay with a flaking surface.  The most affected was the one worked and dried on aluminum, the next was the one dried on aluminum, and the third was only worked on aluminum.  The piece made without contact on aluminum was fine.

Generally, if you are just using a cookie cutter made of aluminum and it is not left in contact with the clay you will be fine.  If you really want to be safe, you can coat aluminum or suspected aluminum cutters with a coat of plastic or varnish.  Make sure all drying and work surfaces are coated or made from non-aluminum metals.

© MED’A Creations & Mary Ellin D’Agostino, 2010