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

 Charms for Charity

The Metal Clay community at large will again officially sponsor the Charms for
Charity Fundraising Event. Metal Clay artists within our own community will create
handcrafted charms for bracelets and necklaces, which will be raffled to raise
money for cancer treatment and prevention. The charities it will benefit are:

American Cancer Society

The Marrow Foundation

Donated charms are due by July 10th. The drawing will be at the PMC Guild
Conference on July 30, 2010.

Checks should be made out to either the American Cancer Society or The Marrow

For more information, go to


CALL FOR RING IMAGES!!! Deadline: November 1, 2010

Hattie Sanderson is pleased to announce that she is writing a book dedicated to
metal clay rings! It will be published by Brynmorgen Press.

You are invited to submit high quality images of metal clay rings for possible
inclusion in the book. Please share this information with your students or
other artists who may be interested. This is a great opportunity to have
your work published. We are seeking rings that range from simple to complex that are of good design and well-crafted. Photographs must be high quality to be considered.

***FREE Copy of book to all artists whose work is included!***

Submission guidelines are available at

If you have questions, please contact Hattie at (815) 393-4365 or email

Spring is here and lots of things are growing, including mold. Questions about mold in metal clay come up regularly this time of year.  Here is probably more than you ever wanted to know about mold in metal clay.

 The health issues related to mold revolve around breathing the mold spores and the mycotoxins they produce. Unless you have allergies, asthma, or other respiratory problems, minor exposure is usually just irritating. Mold is everywhere, so I don’t want to be an alarmist, but some molds are toxic and you do want to take some care (links to info on toxic mold are at the end of this missive). Wear a dust mask when you start working with the moldy clay–if you are “smelling” the musty mold, you are breathing mold spores. If you are sensitive, wear a HEPA grade dust mask. Be sure to wash hands and use a good air filter or positive ventilation to keep from breathing mold dust.

Personally, I am very sensitive to mold and dust and try to open up and do the initial working of moldy clay outside to keep from adding mold spores into my studio. If there is a breeze, I may not bother with a dust mask. I usually scrape off and dispose of the worst of the mold for aesthetic reasons and then knead the clay. Once it is thoroughly mixed in, the chances of getting mold spores in the air is a lot lower, and I take it back into my workshop and try to use it up quickly (within a few days).

Keeping the clay tightly wrapped so no air gets to it will help limit the mold growth as well. White vinegar can be added to kill the mold. Simply add a few drops of white vinegar to the clay and let it sit overnight; small spots of mold will often completely disappear.  Larger incursions may still be visible, but can just be mixed into the clay.

Lavender essential oil also seems to retard mold growth (it may kill it as well).  I haven’t had a problem with mold since I started using the lavender oil.  I add it to all my slip because it makes the slip stick better to both fired and unfired silver clay.

After working with moldy clay, you will want to clean your tools and work surfaces to remove mold spores. Bleach or strong white vinegar can be used to sterilize tools and work surfaces. If you have a HEPA air filter, you should run it in your working area before, during, and after in order to remove as many of the spoors from the environment as possible. These steps may help prevent future mold outbreaks.

The absolute best way to prevent moldy clay is to not let wet clay sit around for long periods of time after it has been opened (factory sealed packages are usually sterile). So use that clay up! Alternately, if you have leftover clay that is pretty dry and do not intend to use it for some time, let it dry out completely and store that way. Dry clay, will not grow mold, but does give you the challenge of reconstituting it–break it up into small pieces or grind it in a silver clay dedicated coffee mill, add (distilled) water, mix, cover tightly, and allow to sit for one or more days to allow the moisture to fully penetrate the binder. After that, it is a matter of kneading (in plastic), and adjusting the moisture content to the desired consistency. Glycerin can be added to make the clay more workable.  Adding a few drops of lavender oil or white vinegar can give you some mold insurance.  Pick your smell!  Other essential oils (such as citrus) will probably do the trick, but I haven’t tested them.

You can also sterilize moldy clay by heating it. This means that you are going to dry out the clay and will have to reconstitute it. To sterilize the clay using heat, you will need to heat it over 130F (56C) for a minimum of 30 minutes. Heat for longer to ensure the entire piece has been sterilized. I usually use my oven or toaster oven to do this at its lowest setting–about 200-250F. A good dehydrator will allow you to adjust the heat to specific temperatures as well and will give good positive airflow. Don’t heat much hotter than this or the binder will begin to darken and burn. To read more about heat sterilization, check out: This is written for heating and sterilizing wood, but will give you a lot of information on sterilization, heating and drying that can be applied to metal clays (or at least their binders). Apparently this is a big issue in the wood pallet industry! Who knew?

Finally, keep in mind that the mold is using the binder in your clay as a food source. If you let it keep growing on your clay, it is degrading the binder. This is probably not an issue unless you let it grow for a *really* long time though! 😉  I had a tub full of moldy clay that has been sitting in my studio for a couple of years and it was still ok to work.  Keep in mind that the binder in the metal clay does start to break down after 6+ years, so any *really* old clay you have should be used as soon as possible.  Don’t let it sit around too long.

If you know that your working environment is contaminated with toxic mold, you need to take appropriate precautions. A quick Google search found the following sources on toxic mold:

I originally wrote this post in February of 2008 for the Metal Clay Yahoo group and have updated it.  It was written with silver clay in mind, but the advice should transfer to the other metal clays as well.  If anyone has additional knowledge regarding mold in the base metal clays, please let me know and I can include it here.  Bronze and copper clays are probably resistant to mold as copper tends to be toxic to growing things—it used to be used in bottom paint for boats to prevent stuff from growing on them, but has been banned because it sheds toxic residue wherever boats are regularly stored.  The replacement paints are not nearly as effective at retarding marine growth.

Send me your questions regarding this and other issues and I will research and answer them.

Mary Ellin D’Agostino 

Summer and the biennial PMC Guild Conference are just around the corner.  PMC Connection has lined up a fantastic set of pre-conference classes that you can take to get you in the right mood for the conference.  This is a great opportunity to take  a certification class or a specialty class.  Classes will run Mon-Wed July 26-28, 2010; the conference runs from July 29-Aug1, 2010.  Here is the lineup:

Bronze Clay by Sherry Viktora
Copper Clay by Sherry Viktora
Custom Stamp Bracelet by Sherry Fotopoulos
Glass Box with PMC Lid by Mary Ellin D’Agostino
Married Metal Clays:  Alloying Silver and Copper Clays by Mary Ellin D’Agostino
Pine Needle Casting by Sharon Gillespie
Silver Screws by Sherry Fotopoulos
Certification Level 1 by Ruth Greening
Certification Level 2 by Peggy Houchin
Certification Level 3 by Mary Ann Devos

For more information or to register go to the PMC Connection Pre-Conference Class Pages.

Heating Up the Relationship: Guidelines For Firing Your Married Silver And Copper Clays, Part 2

Mary Ellin D’Agostino

This is the second part of my report on how to fire metal clay alloys made from silver and copper. For directions on how to make and use these alloys, see the post In Search of Married Metals: Alloying Silver and Copper Clays Project. In part one of Heating up the Relationship, I explained the method for firing alloyed silver and copper clay pieces made using any of the commercially available copper clays. In all tests in part 1, low fire silver clays were used.  In part 2, I will discuss firing alternatives for quick-fire copper clays.

A series of firing tests were performed on both Art Clay Copper and Hadar’s Quick Fire Copper clays. I was excited by the prospect of not having to fire in carbon.

Open Shelf & Torch Tests:
Alas, no-carbon firing is not a good option for mixtures of silver and copper clays unless they contain only the smallest amount of silver or the alloyed clays. Torch firing produced a very weak product in all of the alloy mixtures. Paradoxically, in a complete turn around to alloys made from the first generation copper clays (Metal Adventures CopprClay and Hadar’s “traditional” copper clay), the sterling alloy was very weak and the shibuishi alloys were the strongest. None of the open shelf or torch firing tests resulted in a work product I would consider using in a final product. Even the strongest (the shibuishi alloys) broke when bent as little as 30°. Most of the test pieces snapped long before that point. This was true for pieces torch fired for a few minutes and those kiln fired for as long as 3 hours. The maximum firing temperature for these alloys is approximately 1450°F/788°C. If you exceed this temperature, the pieces melt. See Part one of this series for a discussion of firing and melting temperatures for silver-copper alloys.

An attempt at firing with a Speed-Fire Cone also resulted in failure, but may have been due to not keeping the pieces hot enough as the gas tank was a bit low. If the other results had been more promising, I might have rushed out and gotten a new tank of propane and tried again. Since all the torch and open shelf tests were dismal failures, I have not been in a rush to try again with the Speed-Fire Cone system. If anyone tries it and gets better results, let me know.

No-carbon firing is not recommended for alloyed copper and silver clays. However, it is possible that if you make the piece very thick and don’t need a really strong (bendable) end product, you might be able to use one of these methods. Hadar Jacobson reports some success with a shibuishi clay that she torch fired, but doesn’t go into detail as to how strong her piece was. Click here to go to her report.

Carbon in a Fiber Blanket Box Tests:
Again, both Art Clay and Hadar’s Clay brands of quick fire copper were tested. For a full description of the fiber-blanket box method, see Hadar’s blog on the subject. A box was made of fiber blanket and filled about ¾-1” with carbon. The test strips were placed in the carbon and covered with another ¾-1” of carbon. (All carbon tests have been done with the coconut based carbon).

In the first test (test series C5 & D1), the kiln was heated to 1450°F/788°C and held for 2 hours. Binders were not burned off in advance. Approximately half of the carbon burned away. Pieces came out black and the alloy strips with the most silver melted. Some bending was possible, but the maximum bends ranged from 45° to 90°. Bending beyond this point resulted in the test strips snapping. Results were similar for both brands of clay with one small difference. The Art Clay copper pieces with more than 25% silver melted, while only those with more than 50% silver melted in the pieces made with Hadar’s copper clay.

In the second test (test series D3 & C7), I reduced the temperature to 1425°F/774°C and held for 3 hours. Results were similar to the first. Alloys with more than 25% silver mixed with Art Clay brand copper melted while those with more that 50% silver mixed with Hadar’s brand copper melted. In all cases where the pieces didn’t melt, the metal failed at or before a 45° bend. Again, this firing schedule may be adequate if pieces are thick and are not likely to be subject to much stress.

One complicating factor is that in these final tests (C5-C7 and D1-D3), reconstituted silver clay was used that contained some PMC+ in addition to PMC3 silver clay. This was an economy measure on my part as these tests are getting expensive! If anyone gets better results using only low-fire silver, let me know.

Steel Box & Carbon Tests:
In these tests (test series D2 & C6), the pieces were placed on carbon in a 3.5” diameter stainless steel box, the binder torched off, covered with more carbon, then sealed with a stainless steel lid, heated at full ramp in an Evenheat E91 kiln to 1450°F/788°C and held for 6 hours. These tests also used the reconstituted clay rather than pure and fresh low-fire silver clay. Results are consistent with use of the first generation copper clays (Metal Adventures CopprClay and Hadar’s Traditional copper clay). In these cases, the pieces with more silver were the strongest while those with the most copper were somewhat weaker. Maximum bend achieved before breaking were 45°-90°. An 8 hour firing would probably improve the strength. Firing in a larger box and kiln might also improve matters as I achieved the best results in earlier tests using a large kiln with a significantly larger firing box with a lot more carbon to create a better reduction atmosphere. I will report more after further testing.

Tnanks go to Jackie Truty and Art Clay World for the Art Clay Copper sample.

© 2010 Mary Ellin D’Agostino