DRAFT - WORK IN PROGRESS

Photo of Hadar's Clay metal clay powders courtesy of Hadar Jacobson.

Hadar Jacobson of Textures Studio produces her formula of bronze clay and several other base metal clays in powder form. Hadar's clay base metal clay powders can be mixed fresh on demand, whenever and in whatever quantity desired. You'll find a lot of information about her powdered base metal clays on her blog. There are links to extremely informative PDFs she has written for her Hadar's Clay customers, which she generously has decided to make available to all interested metal clay artisans.

See www.squidoo.com/bronzclay.

Photo of "Bronze Koi with Mold: courtesy of the artist, Kathy Davis. Photographed by the artist.

Hadar Jacobson says of Hadar's Clay, "Shrinkage of flat pieces is obvious while drying. Two-dimensional pieces shrink like low-shrinkage silver clay. 3D bronze pieces shrink less than silver."

Shrinkage in bronze clay appears to be more variable than in silver clay. For example, holes do not shrink as much as outer dimensions, and some shapes seems to shrink more or less than others. The current thinking among some artists is that some of these variations in shrinkage may be caused primarily by incomplete sintering. This theory is difficult to test, however, because even BRONZclay pieces that have not sintered to their maximum density/shrinkage* can be extremely strong, making it hard to tell whether or not a fired piece has sintered all the way through.

*Density and shrinkage during firing are related. An object's density is measured by dividing its mass (weight) by its volume (size). For example, a 1" cube made out of foam has a much lower density than a 1" cube made out of metal, because the foam weighs much less than the same volume of metal.

Keeping good notes
In the bronze clay class I took with Celie Fago, she suggested that we trace the outlines and note the thickness of our pieces at the fresh, dry and fired stages, and to keep notes on how much different sizes, shapes and thicknesses shrink for future reference. If you have access to a photocopier, using it to copy your leather-hard and fired pieces is faster, easier and more accurate. Jot notes on your tracings and/or photocopies and keep them in a file or notebook; they're useful in estimating the shrinkage of new designs or recreating the same or similar pieces at a future date.

Photo of bronze clay pendant courtesy of the artist, Gail Lannum. Photographed by the artist.

It is extremely important to join bronze clay attachments securely, as they are under more stress and are more likely to come apart during firing than joints or attachments in silver or gold metal clay. Joining bronze clay to itself securely - especially if both pieces are leather-hard - requires more pressure for a longer time than joining equivalent pieces of precious metal clay. Here are some tips for making secure attachments in bronze clay:

• To join two pieces both made of fresh clay, dampen a little water on the areas to be joined on both pieces (just enough to dampen the clay), wait a few seconds for the water to be absorbed into the clay, then add more water or paste and hold together firmly, checking after 30-60 seconds to see whether the clay from both parts has bonded together well and stays put securely when you remove the pressure. For extra security, blend the dampened clay from both parts together thoroughly with a rubber- or silicone-tipped shaping tool (such as Colour Shapers®) until the clay from both sides is completely knitted together. If the size, shape or type of joint makes it difficult to blend the two pieces together, use bronze clay paste to help you make a secure and seamless attachment. Let the joint dry, then dampen the seam and "caulk" it firmly with tiny snakes of fresh clay (or very thick paste, if necessary).
• To join fresh clay to leather-hard clay, dampen the areas to be joined sparingly, let the moisture soak in for a few seconds, then use more water or paste to attach the pieces. Remember to maintain constant pressure on the joint until you're sure it will hold together on its own. Dampen the seam after the paste dries and reinforce it with fresh clay.
• To join leather-hard to leather-hard pieces, dampen both pieces at the joint area, let the water absorb briefly, then use thin snakes of fresh clay as "caulk" and press the parts together. Use enough fresh clay so a tiny bit oozes out at the seams to ensure good contact across the entire surface of the join. You can either smooth out the excess "caulking" with a silicone- or rubber-tipped tool now, or clean up the excess after the joint is dry. If you are joining two pieces in the same plane (such as a jump ring or chain link), use a small clothespin to hold the joint closed until it has "taken." Check it under magnification when it's completely dry to see whether any hairline cracks or gaps have developed. If so, dampen them and fill them with additional fresh clay and let dry before firing.
• To make extra-strong attachments between leather-hard pieces, use a "liquid rivet." The "liquid rivet" technique, which I learned from Celie Fago during her "Almost Alchemy" bronze clay workshop, creates extra-strong attachments for difficult joints (e.g., connecting jump rings or other pieces under tension) and joints that require extra strength (e.g., closing rings). To create a liquid rivet, drill small, matching holes in the center of the attachment areas on both pieces to be joined. Dampen both pieces at the joint area (including inside the holes you drilled), wait a few seconds for the moisture to penetrate, then put a little fresh clay between the parts and push them together firmly, so that both holes and the entire seam are tightly packed with fresh clay. Continue to keep pressure on the pieces for at least 2 or 3 minutes, until the fresh and leather-hard clays have knitted together securely. Use enough fresh clay so that a tiny bit oozes out all around the seam to ensure a solid attachment across the entire joint area. You can remove and/or smooth the excess clay around the joint now or sand it away after it is completely dry.
• To join fresh clay to fired clay, do not burnish the metal.(If you have done anything to the surface of the clay after removing it from the carbon, use a small, firm scratch brush to roughen the area where the fresh clay will be attached.) If you are using Hadar's Clay, you can use a little saliva to help fresh clay adhere to the fired clay until it dries, as Hadar Jacobson described in her blog, and then dry the piece on a baking sheet at 220°F-250°F before re-firing. If you are joining BRONZclay pieces, you can paint a little oil paste on the roughened metal before attaching the fresh clay with firm pressure. Oil paste requires a long time to dry. Either let the piece air-dry for several days, or dry it at 90°F for 24 hours as Mardel Rein suggests. Re-fire the piece to sinter the joint area fully.
• To attach partly-dry or fully-dried clay to fired clay, scratch brush the fired part with a small, firm scratch brush where the unfired clay will be attached. Attach the parts together either with thick slip and fresh clay, or with oil paste, if desired (BRONZclay only), and then reinforce with fresh clay after the oil paste has dried. Remember to hold the parts together for a few minutes (or longer, if necessary for a secure joint). Dry joints made with Hadar's Clay on a baking sheet at 220°F-250°F before re-firing. For joints made with BRONZclay, use any of the drying methods in the "Drying Bronze Clay" section. If oil paste is used, either let the piece air-dry for several days or dry it at 90°F for 24 hours. Re-fire.
• To attach two pieces of fired bronze clay, either roughen both pieces in the areas to be joined using coarse sandpaper or a fiber wheel on a rotary tool, or score a cross-hatch pattern with a hard, sharp point (such as a scribe). This gives the metal something for the clay - or oil paste (BRONZclay only) - to grab onto. Attach pieces with fresh clay and feather out the edges of the clay so they're flush with the metal. If you are using BRONZclay, you may use oil paste first and then reinforce with fresh clay, if you wish, or use oil paste only (depending on the join). Maintain pressure on both parts for several minutes or as long as necessary for a secure hold. Dry the joint as above and re-fire.

Photo of Carved Bronze Snake Chain courtesy of the artist, Celie Fago. Photographed by Jennifer Kahn.

Photo of unfired BRONZclay pieces courtesy of the artist, Aja Vaz of Wandering Spirit Designs. Photographed by the artist.

Those of us who have worked with silver or gold precious metal clay know how much easier it is to sand, file, shape and perfect pieces while they are still in their clay state than after they have been fired, when they are pure metal. Nonetheless, most problems or mistakes are not very difficult to correct even after firing. Pure gold or fine silver metal are relatively malleable. They can be formed, reshaped, filed, sanded and even sawn without a lot of time or effort. There are no concerns about oxidation when adding fresh clay, thick slip, syringe clay, homemade lavender paste or Art Clay oil paste to fired silver clay pieces. Roughing up the surface of the metal where the new clay will be added, if necessary, is quick and easy.

Fired bronze clay (i.e., bronze metal), however, is much less forgiving. Many issues, including the hardness of the metal and the inability to re-fire pieces containing both bronze clay and silver clays, make it more important to "get it right the first time" when working with bronze clay. FIred bronze clay certainly can be repaired, and many repairs are just as easy as they would be in silver clay. However, the options are more limited and require much more time and effort than may be used to if you've been working with silver clay.

Take the time to inspect, repair (if needed), reinforce and pre-finish your bronze clay pieces to your satisfaction under magnification before you fire them:

Inspect your bronze clay greenware carefully, under magnification and good light, to identify and repair/reinforce hairline cracks, bubbles, pinholes, gaps in joints, and anything else that can affect the piece's appearance or, more importantly, its structural integrity; any problems are guaranteed to get worse during firing.

To fill gaps or cracks in bronze clay greenware, lightly dampen the repair area with distilled water, let it soak in for a few seconds, and press fresh clay firmly into the crack or seam. Be careful not to trap any air underneath the fresh clay. If the location of the crack of gap prevents you from filling it with fresh clay, use very thick paste instead. Overfill the repair a little to allow for shrinkage as the fresh clay or paste dries; you can sand the excess clay flush with its surroundings once it has dried. If your repair is in the middle of a texture, do your best to recreate the missing texture, using carving gouges, files, Colour Shapers, etc.

Pay special attention to joint seams and attachments, which will come apart during firing if the clay from both pieces is not knitted together securely and reinforced sufficiently in the greenware state. (See "Joining Bronze Clay," above.)

Pre-finish your greenware before firing.There are many methods for pre-finishing the surface of bronze clay greenware, including sanding with salon boards, sanding sponges or sandpaper, burnishing with an agate (or other) burnisher in the areas you plan to polish later, and/or smoothing the surface with a wet wipe or baby wipe. Lora Hart tells her students that the fine level of pre-finishing often recommended for silver clay greenware is not required when working with bronze clay, which "develops a very slight tooth when firing." She says she rarely uses sandpaper finer than 320 grit (and never uses anything finer than 400 grit) on her bronze clay greenware.

Do a final inspection under the magnifier after all repairs and/or reinforcements are completely dry. If you're satisfied with how your piece looks under magnification, you're likely to be pleased with it after it's fired.

I encourage you not to rush or skip these steps. Being patient and disciplined about inspecting, repairing and reinforcing your bronze clay in the greenware state will pay huge dividends in both the structural integrity and the appearance of your finished bronze pieces.

The most dramatic difference between working with precious metal clay and base metal clay is the firing process, which requires a different firing container, firing environment, and firing schedule.

Experiments continue in search of optimal, reliable firing schedules. Temperature adjustments of even 10 degrees Fahrenheit can mean the difference between perfectly sintered bronze clay pieces and under- or over-fired ones. Keep detailed notes so you can tweak any schedule to suit your own kiln.

The type of kiln matters much more when firing bronze clay than when firing silver or gold clay. Not all kilns were designed to maintain high temperatures for many hours at a time. Repeated nine-hour firing cycles can shorten the life of your kiln. Be sure to ask the manufacturer of your kiln (or a knowledgeable supplier) what effect bronze clay firings are likely to have on it. Also, the type of kiln you have should be taken into account in determining your optimal firing schedule(s). Kiln brick retains heat much longer than fiber/muffle walls. Top-loading (brick) kilns have firing elements on all sides for better heat distribution vs. front-loading (fiber/muffle) kilns, which have elements on only three sides.

Covering the firing pan with a lid is not required, but doing so minimizes the amount of carbon lost to ash during firing.

Recommended Firing Schedules for Bronze Clay
See www.squidoo.com/bronzclay.

Note: BRONZclay and clay mixed from bronze clay powder are made from different formulas and therefore do not behave identically, especially when it comes to firing and sintering. The following firing schedules were developed for Hadar's Clay only.

Recommended Firing Schedules for Hadar's Clay

See Hadar Jacobson's blog for detailed firing instructions.

Photo of carved bronze clay bangle courtesy of the artist, Barbara Becker Simon. Photographed by the artist.

Pieces made from bronze metal clay are more likely than their silver clay counterparts to develop cracks or fissures during firing, or for trapped air inside the clay to create unsightly bumps on the surface or, far worse, to weaken the structural integrity of the metal and cause cracks or breaks sooner or later.

Repairing fired bronze clay - filling holes or cracks, reattaching broken pieces, etc. - is very similar to making the same repairs in silver clay. If bubbles, holes, cracks or joint gaps have developed during firing, repair the metal in its "pristine" state straight out of the kiln. If problems develop after you have finished the piece (e.g., a bubble is uncovered during sanding or filing), then clean the area to be repaired thoroughly with coarse sandpaper or with a fiber wheel on a rotary tool or flexshaft. If you need to reattach two separate parts that have broken apart and plan to reattach them with fresh clay, you also may want to score the metal with a scribe, needle tool or other sharp tool to create some "tooth" for the new clay to grab onto.

To repair, reattach or reinforce fired pieces using Hadar's Clay:
Make repairs similarly to the way you would with silver clay. For the strongest attachments, use fresh clay (vs. paste or re-using scrap clay). Hadar suggests using saliva to help her fresh clay adhere to the bronze metal while it is drying. Dry on a baking sheet at 220°F-250°F and re-fire. Hadar recommends this great time-saving method for re-firing repairs: Fire the repaired area with a torch for about 30 seconds instead of the first phase of the firing schedule, then move directly to the second phase of the firing schedule.

To repair, reattach or reinforce pieces using BRONZclay:
Use fresh clay straight from the package that has been conditioned and wedged (vs. re-using scrap clay). If you need a slightly moister consistency, you may mix a little water into the fresh clay to be used for the repair. If you wish, you may apply a little BRONZclay oil paste to the prepared repair area on the metal before adding the fresh clay. Make sure the fresh clay (and oil paste, if used) is completely dry before re-firing. (Use the firing schedule for thicker pieces when re-firing.)

For repairs to either formula of fired bronze clay: Remember that the fresh clay will shrink as it dries and as it fires. Either overfill your repairs slightly or plan to re-fill and re-fire your breaks, cracks, holes, etc. a third or fourth time, as needed, so the repaired area is flush with the rest of the piece.

When one of Barbara Becker Simon's pieces breaks, she "makes lemonade from the lemons" by approaching the repair as an opportunity to add a new design element. When one of her carved bronze clay bangles broke, Barbara reattached the pieces with large cubes of fresh clay, allowed them to dry, and carved them to complement the rest of the design before re-firing. (You can see the repaired bangle with the added carved, cube-shape "nodes" at the beginning of this section.) By turning the problem into an opportunity, she actually enhanced the original design.

Barbara explains that "the reason these 'boxes' worked is that the new clay surrounded and clamped on to the ins and outs of the nasty break, thereby covering up all the ugliness and making a joint that was secure. Even though I accounted for shrinkage by making the nodes larger, I still had to go back and re-caulk and re-fire cracks that developed on the boxes, in some cases more than once. But I felt it was worth it to save a piece on which I worked a long time." Although Barbara added cubes of fresh clay because they went well with her original design, these added "nodes" can be any shape you wish.

Adding fresh clay "nodes" when reattaching broken fired pieces isn't Barbara's only approach to making creative repairs. The larger bangle shown below illustrates another way to fix a piece that, at first, might seem beyond repair. Barbara was trying out a faster firing schedule with this bangle, with the result that one of the large rectangular cubes "just completely took a dive." Her fabulous bracelet represented a lot of work, so she is salvaging it by grinding down the ruined front and back surfaces of the cube, and she plans to create new "faceplates" (my term) that she will rivet on later.

Photo of large carved bronze clay bangle courtesy of the artist, Barbara Becker Simon. Photographed by the artist.

Re-firing pieces from a pair or matched set:
Re-fire both/all the pieces, not just the one(s) you repaired, so that any incremental shrinkage in the second firing will affect all the matching pieces in the set.

Important: Never re-fire pieces that contain both bronze and silver! See the section on Combining Bronze Clay and Silver Clay for more information.

Photo of bronze and silver clay Blouse courtesy of the artist, Hadar Jacobson of Textures Studio. Photographed by the artist.

Shaping
Bronze clay is extremely hard after firing and cooling, if the pieces have sintered fully in the kiln. Lora Hart explains that bronze becomes heat-hardened if it is heated to a high temperature and allowed to cool slowly. If you need to shape the bronze metal, she recommends annealing it first by either quenching or crash cooling the hot metal rapidly. Celie Fago advises her students to leave the firing pan in the kiln after the heating cycle is complete (cracking the door open, if they wish) until it has cooled to below 300°F, remove the pieces from the carbon, and let them cool to room temperature. If annealing is needed, reheat the metal with a torch to a dull red and quench it.

Finishing fired bronze clay (unlike finishing fired silver clay) is entirely optional. Pieces look great straight from the kiln.

If you want a different finish, or if you want contrasting finishes (for example, wire brushing for a soft satin finish or polishing the high points on a texture), you can use most of the same methods as you would use on fired silver clay. The main difference is that finishing bronze clay requires more time and effort, because bronze is a much harder metal than silver.

Wire Brushing
If you plan to wire brush a fired bronze clay piece to achieve a satin finish, use a soft brush with stainless steel bristles (not brass bristles as you would use on fired silver clay).

Polishing and Tumbling
There are many options for polishing your bronze clay pieces. Here are a few:

• You can use a mild abrasive, such as pumice, for a soft, not bright, shine. Dip a damp finger or a baby toothbrush into the pumice powder and rub the metal in small, tight circles until the desired shine is achieved.
• Polish bronze clay pieces with 600-grit (gray) micron-graded polishing paper.
• Use 3M micron radial bristle disks.
• Use silicone or rubber polishing wheels and points.
• Burnish your pieces in a tumbler, if you wish, just as you would tumble silver clay pieces.

Photo of bronze fence bracelet courtesy of the artist, Celie Fago. Photographed by Robert Diamante.

Patinas Straight From The Kiln
Firing in coconut shell-based activated carbon leaves a natural gold-brown patina, and firing in coal-based activated carbon can result sometimes in beautiful and colorful but unpredictable patinas. (These colors generally appear after the third through the seventh firings; the most colorful effects tend to be produced during the fifth and sixth firings.)

Kiln patinas from coal-derived activated carbon can be vibrant, Aja Vaz's BRONZclay trio pieces:

Photo of BRONZclay trio courtesy of the artist, Aja Vaz of Wandering Spirit Designs. Photographed by the artist.

Or they can be softer and more delicate, as in Celie Fago's bronze lentil pendant:

Photo of bronze lentil pendant courtesy of the artist, Celie Fago. Photographed by Jennifer Kahn.

or Lorena Angulo's "Arbol de Vida" pendant:

Photo of "Arbol de Vida" pendant courtesy of the artist, Lorena Angulo. Photographed by the artist.

If you don't like the patina on your bronze clay pieces after firing them, especially if you're using coal-based activated carbon media, the easiest thing to try first is simply to re-fire them along with your next load of bronze clay greenware. To paraphrase Forrest Gump's mama, firing bronze clay "is like a box of chocolates. You never know what you're gonna get." And the ugly or dull colors from the first firing are guaranteed to change (unpredictably as always), so there's a good chance that whatever you put into a second firing will come out looking better than it went in. There's no downside to trying it, and if you still don't like what you see you always move on to other heat- or chemical-based patinas.

Somewhat More Controlled Heat Patinas
While the untreated patina of bronze clay straight from the kiln can be very attractive, it is completely out of your control. If you wish, you can use methods of heat-coloring that give you some degree of control over the colors that develop. The metal can be heated in several ways, the most popular of which is with a torch.

One technique is to warm the metal with a torch and then air cool it, repeating until you reach colors you like. Deb Jemmott says she gets the best results by burnishing her fired bronze clay and then heating it very gently on a charcoal block. She advises to heat around the piece, because the burning charcoal creates a reducing atmosphere (similar to that of the charcoal in the stainless pan in the kiln, but to a lesser degree). Use the flame to heat the charcoal (and, indirectly, the metal). Heat a little, then pull the torch away and watch the colors develop. Repeat the process of heating briefly, removing the torch, and watching the colors develop until you see colors you like. Remember that the colors will continue to develop after you pull the torch away; Deb says "if you see the colors while the torch is on the piece, it is too hot and when you pull the torch away, the colors will be gone."

Another approach is to heat the metal until you like the colors and then quickly quench it in cold water or ice water. Air cooling and quenching produce somewhat different results, so you may want to make two test strips and heat both with a torch, air-cooling one and quenching the other in cold water so you can compare the colors.

Beverly Gallerani flame-colors her bronze clay pieces selectively. She places a brushed and tumbled piece on a steel bench block with only a small section she wishes to color hanging over the edge of the block. She heats just that small, overhanging section from the underside, moving the torch flame in slow circles. She watches carefully, cautioning that "the colors can develop quite suddenly," then removes the heat quickly the moment a pleasing color appears and quenches the piece in cold water. Bev finds that, as long as she keeps the heat away from the areas she has colored already, she can place the quenched and dried piece back on the bench block and color a different area without affecting the colors she developed previously. Her "Catch the Wave III" pendant shows one of her torched patinas:

Photo of "Catch the Wave III" courtesy of the artist, Bev Gallerani of Mango Tango Designs. Photographed by the artist.

Even if you over-torch a piece, it still can be salvaged (maybe even improved!) by re-firing. Judi Weers has gotten good results by wire brushing, and burnishing or tumbling such pieces until shiny and just tossing them back in the kiln with her next load of bronze clay. She used this technique very successfully after she had accidentally kept her torch on some bronze clay charms for too long so that they had turned black from surface oxidation. After re-firing them with her next load, the charms came out of the kiln with a beautiful deep gold and pink patina!

A torch is not the only way to heat-color your bronze pieces. Susan Dilger sometimes adds a heat patina by warming her fired bronze clay pieces on an uncovered UltraLite beehive kiln that has been pre-heated for 15 minutes. She kiln-colors only one piece at a time, watching it very closely while heating it and removing it from the UltraLite to cool the instant she begins to see a color she likes (since the colors will continue to develop a bit as the metal cools). Alternatively, as with torch coloring, pieces that are heat-patinated on the UltraLite can be quenched to retard further color development, although quenching after heating does result in a somewhat different patina.

Chemical patinas for bronze clay

Caveat: Breathing any type of chemical fumes can be hazardous to your health. Some chemicals are worse than others in this respect. Make sure you read the warnings on the label before using any chemical, and always work in a ventilated area. You may want to wear a respirator also when using these chemicals.

Liver of Sulfur (LOS) patina
Liver of Sulfur can be used as a patina on bronze clay. In her book "Silver and Bronze Clay: Movement and Mechanisms", Hadar Jacobson explains that, although you cannot get the range of colors on bronze clay that you can on silver, a Liver of Sulfur solution can be used to achieve a dark gray (almost black) patina on bronze. She recommends dipping fired bronze clay quickly into the patina solution and then into cold water, dipping alternately in patina and then in water just until you reach the desired darkness, then immediately rinsing your piece thoroughly in cold running water. She warns that if the bronze is left in the solution rather than alternately dipping in the patina and rinsing, the patina will be very difficult to remove from the areas where you do not want it.

Some artists use a paintbrush, toothpick or cotton swab to apply patina only where they want it, rather than dipping and rinsing, to avoid having to remove the patina from the rest of the piece afterwards.

I and many others were taught to neutralize the patina after achieving the desired color by placing the piece in a saturated solution of baking soda and water, which stops the chemical reaction with the metal. Rinse thoroughly under cold running water.

Coloring with ammonia fumes
In Celie Fago's Almost Alchemy bronze clay class, which I attended in September 2008, she told us about using ammonia fumes to add bright blue and blue-green patina colors to fired bronze clay pieces.

"Blue Bronze Pendant" by Celie Fago courtesy of the artist. Photographed by Jennifer Kahn.

The bright blue patina in Celie's Blue Bronze Pendant, shown above, was made by fuming the bronze piece over plain household ammonia. Here's how Celie describes the process: "You can add salt to the ammonia for a bit more green in the blue but here I used only household ammonia. Suspend the piece over (not touching) an inch or two of ammonia in a glass jar with a lid. Either drill small holes in the jar lid to pass a wire through or work it out so the jar lid will close over both ends of the wire on which the bronze piece hangs. Leave it to fume until you like the color, anywhere from 24 hours to 10 days. It is wise to open the jar slowly, and out of doors, as the ammonia fumes build up and you won't want a big whiff of it."

For more information on induced patinas, Celie highly recommends "The Colouring, Bronzing and Patination of Metals" by Richard Hughes and Michael Rowe.

Photo of bronze clay pendant with Australian opal courtesy of the artist, Delores Highsmith. Photographed by the artist.

You can set CZs, lab-created stones and some sapphires and rubies (corundum) in bronze clay as long as they can survive the prolonged high temperatures. Not all of them can (or not without changing color). For silver or gold metal clay designs, it's easy to simply include a loose stone in a firing load to see whether it survives the firing. With bronze clay, that method is impractical (imagine searching for your loose CZ in a panful of carbon firing media!). So be sure to buy from a reliable metal clay supplier or a supplier who will guarantee certain stones and colors as being safe to fire in metal clay.

Some heat-sensitive stones that cannot be fired successfully in silver metal clay can be fired successfully in bronze clay when buried in carbon to protect them from atmospheric oxygen. For example, in her excellent article "BRONZclay - How To Fire Bronze Clay", Mardel Rein of explained that in her tests, tanzanite-colored CZs - which normally can be heated only to 1100F or less for no longer than 10 minutes before they start to darken - survived two separate, nine-hour firings (for a total of 18 hours) at 1550F in activated carbon with no change in the color or brilliance vs. the unfired control sample. She concluded that "it's oxygen that causes the problem in heating this type of stone, not the actual heat itself." Celie Fago has fired diamonds successfully in bronze clay.

When embedding stones in bronze clay or making bronze clay bezels or other settings, remember to allow for shrinkage, especially in height/thickness. Embed fireable stones deeper in bronze clay than you would in silver or gold clay:

• Set faceted stones so that the table (top surface) is below the surface of the clay. A tip from Lora Hart: Gem setting burs clog easily when used on bronze clay greenware and should be cleaned frequently while making deep holes for faceted stones.
• For cabochons, press the stone into the clay until less than half the height of the stone remains exposed above the clay.
• To prevent carbon granules from getting between a stone and its clay setting, cover the stone and the setting with a small piece of kiln shelf paper (AKA fiber paper), such as ThinFire paper, before adding the next layer of activated carbon granules. Cut the paper just large enough to cover the stone and the setting - no larger - so you don't create unnecessary air pockets when the next layer of carbon covers it.
• Remember that smaller clay bezels will shrink proportionally more than larger clay bezels. If you wish to set natural gemstones or other stones that cannot survive the bronze clay firing conditions, you may be able to embed fine silver bezel cups successfully (see Embedding Wire, Findings and Settings in Bronze Clay, above).

Photo of bronze clay butterfly pendant with pod courtesy of the artist, Judi Weers of Cardinal Creations. Photographed by the artist.

Bronze clay must pieces be thick enough to support their own weight.
Like high-shrinkage Original/Standard PMC, bronze clay is affected by gravitational pull more than medium- and low-fire silver clays. For this reason, hollow forms should be made thicker in bronze clay than equivalent pieces in silver clay. For example, Celie Fago recommends rolling the clay for small lentil beads (less than 1-1/4" in diameter) at 4 to 5 cards thick, and rolling larger lentils at 6 to 7 cards. Mardel Rein's article on Getting Started with BRONZclay also provides some helpful guidelines in determining how thick bronze clay pieces need to be in order to support themselves without collapsing under their own weight.

Hollow forms in bronze clay should be fired in an orientation that minimizes the likelihood of distortion or sagging during the firing process (e.g., positioning lentil beads vertically in the activated carbon granules but placing domed discs horizontally with the opening face up in the carbon, like a bowl).

Armatures vs. cores
Armatures are dimensional structures that help to form and support "wet" clay until it has dried. Cores are armatures enclosed within the clay during firing. Combustible cores burn out, partially or completely, during firing. Non-combustible cores are enclosed permanently.

Using armatures to create hollow forms
It's fine to use temporary armatures while shaping and drying bronze clay. You can create enclosed hollow forms by making them in two or more pieces and then attaching them when all pieces are dry, or by using a freeform hollow construction technique developed by J. Fred Woell which involves draping rolled-out clay loosely over an armature, lifting the clay off the armature when dry, sanding the open edges in a flat plane, and then attaching it to a sheet of freshly rolled-out clay to close the form. Fred wrote an entire chapter explaining this technique in the book, "PMC Technic".

Using combustible cores
Combustible materials burn only in the presence of oxygen, so they do not burn out much during a bronze clay firing under carbon.

Hadar Jacobson has found that combustible cores, including dry pasta, can be fired successfully with a two-phase firing schedule: "If you cover it with just a little carbon and fire without a lid for the first phase of the firing schedule, it will burn just fine."

The new experimental firing schedule for BRONZclay also enables artists to use combustible cores successfully, since the cores burn out during the initial open-air firing before the pieces are fired under carbon. The substantial oxidation that takes place during the air-firing is reversed during the subsequent firing under carbon. This means even combustible materials like cork or wood clay can be used successfully as cores for BRONZclay.

Some artists have found that thin combustible cores, such as leaves or seed pods, or combustible cores that have some "give", such as white glue-coated breakfast cereal or snack puffs, work fairly well with bronze clay, especially if there is at least one opening in the clay (e.g., bead holes). Celie Fago uses Kix® cereal or cheese-flavored snack puffs coated with Sobo® glue as combustible cores for small beads in both bronze and silver clays. She sometimes wads together multiple glue-coated pieces of Kix or cheese puffs to form larger combustible cores in various shapes. She covers the glue-coated cores either with multiple layers of very thick bronze clay paste or with rolled-out lump clay to form hollow-core beads.

Non-combustible firing supports
Small pieces of fiber blanket can be used to support shapes that aren't completely enclosed during firing,

Non-combustible size/shape placeholders
In general, non-combustible size/shape placeholders are not recommended for use with any high-shrinkage clay, including bronze clay. The clay will crack or break when fired around investment, plaster or Creative Paperclay plugs, such as ring sizing pellets, flat placeholders (e.g., for cabochons) or modeled cones of faceted stones or other items to be set after firing. If you wish, you can use a small rolled-up piece of kiln blanket inside a ring shank as a kind of sizing plug, although the very quality that allows it to be fired inside an enclosed circle - its ability to be compressed - limits its usefulness as a sizing plug.

Photo of "Bronze Knuckles" ring courtesy of the artist, Jennifer Kahn. Photographed by Robert Diamante.

The safest way to combine bronze clay and silver clay in the same design is to fire the components separately and then join them either with solder or with cold connections.

Many types of cold connections are possible, and can be incorporated in your design to advantage. Rivets, tabs and jump rings are common choices. One of the most innovative approaches to cold-connecting bronze and silver clay components was developed by Jen Kahn for her "Modern Relics" design series. Jen, who wrote a terrific chapter about her bezel setting techniques in "PMC Technic", makes and fires bronze clay components designed to be bezel-set in fired PMC pieces. For her "Bronze Knuckles" ring (shown in the photo above), she created a bronze clay "stone" to set in her silver bezel.

If you have a high tolerance for risk, you may want to try some of the following methods for firing bronze clay with already fired silver clay.

In Hadar Jacobson'sbook, "Silver and Bronze Clay: Movement and Mechanisms," she covers this topic in great detail. In my opinion, this is a must-have book for anyone who wants to work with bronze clay. Hadar has done extensive testing concerning co-firing of bronze and silver clays. While this lens will not attempt to cover this topic in detail (for that, you need to buy her second book), I have highlighted some of her key findings here. Note: While the initial co-firing experiments that Hadar published in her book were done with BRONZclay, not her own Hadar's Clay, the co-firing guidelines apply equally to both brands' bronze clay formulas.

1. Unfired bronze and silver clays cannot be fired together successfully. One (preferably the silver clay*) must be fired first.

2. Bronze clay can be fired successfully over previously fired silver metal clay as long as the bronze clay covers more than 50% of the surface of the fired silver metal clay. While adding bronze clay to fired silver clay is preferable, it also is possible to fire torch-fire silver clay over previously fired bronze metal clay, as in Hadar's beautiful Bag pendant, below. Do not kiln-fire the silver clay over the fired bronze.*

Photo of silver and bronze clay bag with garnet beads courtesy of the artist, Hadar Jacobson. Photographed by the artist.

3. Bronze clay also may be successfully co-fired with already-fired silver clay as long as the pieces are not in contact during firing and there are "not too many" silver pieces in the firing container with the bronze. If you are firing bronze clay links with already-fired silver clay links, alternate the orientation of the links, as usual (one vertical, the next horizontal, the next vertical, etc.) and keep the chain relaxed, making sure that carbon granules separate the links and there is no contact between the links during firing.

4. Another way to prevent contact between the bronze clay and the previously fired silver clay* (or, if necessary, between the silver clay and the previously fired bronze clay) during firing is to separate them either with pieces of Thin-Fire (or other fiber paper) or with a thin layer of Creative Paperclay (which is made from volcanic ash and can be removed easily after firing). By separating the metal clay from the metal with fiber paper or Creative Paperclay, you can create metal clay "spinners" that, when fired, will spin freely around other parts. For example, both Hadar and Celie Fago have made spinner rings consisting of a thinner bronze metal clay band or bands that spin(s) freely inside a channel in a wider, previously-fired silver clay band. Two-tone spinner beads are another popular use for this technique.

*The presence of bronze metal clay (fired or unfired) and the reduced-oxygen firing environment required for bronze clay inhibit silver clay from sintering completely. Therefore, whenever possible, the silver clay components should be fired first, using silver clay firing methods and firing schedules, to ensure full sintering of the silver. The second firing, after the bronze clay is added, should be done using bronze clay firing methods and firing schedules.If silver clay is fired over bronze clay, torch-fire the silver components (do not kiln-fire them).

If your design calls for the bronze clay component to be fired first, Hadar has developed a technique for creating a semi-invisible silver clay "tube rivet" to connect the silver clay component to the fired bronze clay component. (The tube rivet is invisible from the front, but visible from the back.)

• Make the bronze clay component and cut a hole for the tube rivet. Dry, fire and cool the component.
• Cover the entire surface of the bronze metal, including the inside of the rivet hole, with Paperclay paste (Creative Paperclay mixed with a little water). Hold it with cross-lock tweezers as you apply the paste. Dry it on a mug warmer. Continue to add and dry additional paste until the none of the bronze is showing. Remove the tweezers and fill in the "bald" spots with additional paste to hide the bronze metal completely.
• Create the main silver component (no hole), a tube that will just fit inside the hole in the fired bronze component, and a flat disc considerably wider than the diameter of the tube using silver metal clay. Dry these to the leather-hard stage.
• Attach one end of the tube to the main silver greenware component with thick silver clay paste. When it dries, slide the Creative Paperclay-coated bronze component onto the tube and make a pencil mark on the tube where it exits the hole in the bronze component. Make another mark slightly beyond the first one and file/sand off the excess length of the tube.
• Reinsert the tube through the hole in the bronze component, then use thick silver clay paste to attach the disc, centering it over the tube. Let the silver paste dry.
• Torch-fire the silver.
• Wash the bronze component in water to remove the Paperclay paste residue.

Photo of bronze clay, polymer clay and brass wire ring courtesy of the artist, Ronna Sarvas Weltman. Photographed by Doug Yaple.

In her article "BRONZclay - Getting Started With Bronze Clay", Mardel Rein tells us that copper, brass or bronze wire or findings may be embedded in bronze clay and fired in place successfully. She advises against embedding fine or sterling silver wire, findings or settings in bronze clay because the metals will attempt to alloy with each other, with ugly (and often worse) results. Many artists have discovered that part of the metal can appear to be "eaten away" in the alloyed areas. Not good!

In Hadar Jacobson's blog, she says that in her experience, bare copper wire embedded in base metal clay will break when bent after firing, but that bronze wire can be embedded and fired successfully. In her book "Silver and Bronze Clay: Movement and Mechanisms", she says fine silver bezel cups may be embedded into bronze clay as long as the proportion of fine silver to bronze clay is small. (In other words, don't embed a fine silver bezel cup into a piece of bronze clay that isn't significantly larger in diameter than the silver cup). Also, the bronze clay must be thick enough for the bezel cup to be embedded fairly deeply, since bronze clay shrinks more than silver clay. In her book, Hadar recommends using the inverted bezel cup to cut a perfectly-sized hole for embedding the bezel. She says that the bezel may be soldered in place if necessary (i.e., if it pops out of the hold after firing).

Alternatively, you can design in such as way as to give the appearance of embedded wires in bronze clay, as in the unusual bronze clay, polymer clay and bronze wire ring by Ronna Sarvas Weltman shown above. Ronna created the circular bronze clay "frame," then made a wide polymer clay shaped disk with a small hole in the center. She made a triple ring shank from bronze wire, leaving one end of the wire sticking up from the band, then threaded on the disk and bent the wire end. The bronze clay frame was centered over the wire and filled with black polymer clay.

Note: not all "bronze" wire is real bronze.
Some wire that is sold as "bronze" may be bronze colored brass (an alloy of copper and zinc) rather than true bronze (which is an alloy of copper and tin.) Brass wire that has been treated to look like bronze may not retain its bronze color over time or if heated. You may want to ask your wire suppliers about the alloy from which their "bronze" wire is made so you know what you're using.

Suppliers that carry true bronze include Cool Tools, Rio Grande, Whole Lotta Whimsy, and Metal Clay Supply.

Photo of "Hinged Fence Bracelet" courtesy of the artist, Hadar Jacobson. Photographed by the artist.

Bronze clay lends itself beautifully to making hinges. The most obvious reason is that after the clay is fired, the bronze metal is extremely strong and durable. Another reason may be less obvious: a hinge is made of tube shapes, which tend to shrink very little in their interior diameter after firing, which makes it easier to estimate the gauge of the wire that will be needed for the hinge pin.

The most important thing to remember when making hinges from bronze clay is to make sure the hinge tubes are attached to the pieces they are joining extremely securely, and reinforced well with additional fresh clay after the original attachment has dried.

For a great way to practice making bronze clay hinges, try the Hinged Bronze Fence Bracelet project from Hadar Jacobson's book, Silver and Bronze Clay: Movement and Mechanisms shown above.

Elaine Luther, owner of Creative Texture Tools and author of the excellent blog All Things Metal Clay, has set up a Bronze Clay Pool group on Flickr where metal clay artists can posts photos of their bronze clay pieces. I encourage you to click on the link to view many wonderful bronze clay designs by talented metal clay artists, and to share your own work in bronze clay.