Precious Metal Clay
© Rio Grande

 

An Introduction to the Material, Tools and Techniques of Working with Precious Metal Clay

 

What is PMC?

Precious Metal Clay represents a dramatic development in the handling of precious metals. PMC consists of microscopic particles of silver or gold suspended in an organic binder to create a pliable material with a consistency similar to modeling clay. PMC can be worked with the fingers and simple inexpensive tools to create a vast range of forms and surfaces that would be unattainable or laborious with traditional techniques.

When heated to a high temperature, the binder burns away and the metal particles fuse to form solid metal that can be sanded, soldered, colored and polished like conventional material. This booklet describes some of the techniques devised for PMC and will guide you through your first firing experience.

History

Precious Metal Clay was developed by scientists working at the Mitsubishi Materials Special Products division in Sanda, Japan. After years of experimentation the first patents were awarded in the early 1990s with many additional materials joining the family of products. The principle ingredient of PMC is gold or silver, reduced to tiny flakes smaller than 20 microns in size. As a point of reference, it would take as many as 25 of these particles clumped together to equal a grain of salt.

The other ingredients in PMC are water and an organic (naturally occuring) binder. After firing, the water and binder have completely burned away so what remains can be hallmarked as .999 silver or gold.Dried out or unwanted objects can be refined just like conventional precious metal.

How Does It Work?

Under the proper conditions, crystals of metal fuse together in the same way that droplets of water run together to make larger puddles on the window pane. In the case of metals, oxides (tarnish) that form naturally on most metals prevent this from happening. The solution here is to use precious or noble metals in their pure state. These do not readily oxidize so even at the high temperatures needed to induce fusion they remain free of coatings. This explains why there is not a brass or sterling version of PMC - short of firing in a vacuum it won't work.

Form

Using very simple tools and your own very talented fingers, PMC is rolled, pressed, squeezed, layered and molded into a desired shape. Parts can be added, removed and refined as you go, making this a spontaneous and liberating process.

Fire

After it has dried, the PMC object is taken to a specific heat (as described on page 9). This drives off whatever moisture remains, then burns the binder. This goes off as a harmless smoke. At this point the PMC is a fragile porous metallic husk. At higher temperatures the particles melt into one another to form a solid dense metal. Depending on the type of PMC, this can take from 10 minutes to two hours.

Finish

After firing, the object can be handled like any other gold or silver item. It can be soldered, burnished, buffed, tumbled, plated, etc. to achieve whatever finish you want.

Three Kinds of PMC&ldots;

The Original! This version has the best working properties and remains moist a bit longer than the others. It shrinks 28%, so textures and details are enhanced after firing. Objects made on original PMC remain slightly porous even after proper firing. This means they are lighter than the same size object made of wrought silver, but also means strength is reduced.

This version, called "PMC Plus" is made of a differently shaped metal particle and contains less binder. The shrinkage rate is 12-15%. PMC+ offers three distinct firing options, two of them at lower temperatures than the original. Objects made of PMC+ can go from clay to metal in as little as 10 minutes. This material is about 10% more expensive than original PMC because of increased material costs.

PMC3, the third member of the family, is as dense as PMC+, fires as fast, but does all this at remarkably low temperatures. Three distinct firing options provide a range that makes this especially useful for co-firing glass, findsings and some stones.

&ldots; Available in Several Forms

Lump

The most popular form because from here you can make sheet, wire, paste and volumetric forms.

Slip

This material is specially formulated to allow it to be pressed through a nozzle. If you have ever decorated a cake you can master PMC Slip. Sold loaded into a disposable syringe.

Paste

A thick slurry that is used to fill joints, adhere parts and create luscious frosting-like surfaces.

Paper

Mitsubishi developed this for the Japanese art of origami, but American artists have found this thin leathery sheet useful for weaving, braiding and to create drapery effects.

Sheet

Thick version of the paper, excellent for rings, backing plates, medallions and more.

nge that makes this especially useful for co-firing glass, findings and some stones.

Suggested Handtools

Basics

Sheets of plastic or glass make terrific and portable work surfaces. Use mylar sheets, page dividers or plastic signs. Most PMC artists start with this:

dish with sponge for water
paintbrush
plastic tube as a roller
straws (for making holes)
needle tool
palette knife
rubber-tipped color shaper
ruler
toothpicks

Specialty Tools

As your insterest grows you'll find yourself adding tools to your collection. In addition to your own discoveries you might find these useful:

tweezers
tissue blade
magnifiers
stiff flat brush (for smoothing)
rubber stamps
texture plates
small chisels
playing cards (spacers for thickness)
files
manicure sanding boards
plastic design templates
blacking patina solution

Basic Techniques

Put a few drops of olive oil on your palms before starting; this will help keep the clay moist. To make sheets, use a roller as you would for pie crusts. To make a uniform thickness, set two equal stacks of playing cards on each side of the lump. Thicknesses of 3-6 cards is typical for jewelry items.

A kitchen knife, an X-Acto blade or the edge of a card can be used both to cut pieces and to lift them off the sheet. When joining parts, set them close together and apply a drop of water with a pointed brush. Allow this to penetrate for a few seconds then press the parts together. It's that easy!

To achieve rich textures, either press the PMC against a rough surface or roll the surface over a sheet of PMC. Even simple objects like bottle caps leave interesting trails, and natural objects like leaves, bark and wood offer many possibilities.

One way to make a loop for a pendant is to roll out a rod that you then form in a loop. Cut off the ends to make a solid attachment, moisten with water and press into position. Another way is to cut a crescent in the edge of the piece and press a ball of clay into that space. Poke a hole with a needle tool or a straw and then after firing feed a loop through that hole.

Most work is done with moist clay but it is also possible to work with PMC after is has dried. You might want to get the general idea of a form then refine it with carving tools or files when it is leather hard. To join parts at this stage either use slip or a household glue.

If the PMC becomes dry as you work, spray or brush on a little water (not too much!) and cover it with plastic wrap for a few minutes to allow it to rehydrate.If you accidentally add too much water just set the PMC aside loosely wrapped and allow it to dry out.

To make rings, wrap tape around a dowel to create the correct size (i.e. 12% larger than the intended final size). Cover this with plastic wrap and work on this form. When the ring is finished, preferably before it has dried, slide it off.

Allow the work to air dry or with speed up the process with a hair dryer, on a heater, or in a slow oven. To allow air to reach all sides, set work on a screen, a wad of paper towel or a piece of foam rubber.

Using Sringe and Paste

PMC Slip comes pre-loaded in a plastic syringe, ready to use. Clip off the tip with scissors to create the size nozzle you need, remembering that the PMC will shrink in firing. The possibilities of using syringe are enormous, and here are a few thoughts to get you started.

Decoration

Use the syringe to make trails that curl and loop around your designs. Particularly when the work is blackened and polished, these make the surface more active andinteresting.

Stonesetting

Press a lab-grown gem into position and trap it with a network of threads from the syringe.

To Make a Net

On a sheet of plastic, squeeze out a series of lines, say 1/4" apart. Cross this with a similar series at a right angle. Return to the first direction and lay threads of PMC between the first lines, then repeat in the second direction. The effect will appear woven.

For Repairs

Because of its handy dispenser and strength, use PMC+ slip to attach parts, repair breaks and reinforce delicate areas, for instance where a loop attaches to a pendant.

On Ceramics

Both syringe and paste bond to glazed or unglazed ceramics. Be certain the surface is clean and apply the PMC firmly enough that there are no air spaces beneath it.

For Transitions

Use paste to fill between elements when creating an organic effect.

Molds, Hollow Forms & More

PMC lends itself easily to working with molds, either commercially made or molds you make yourself. These allow for repeated elements and the production of multiples. Hollow forms allow your work to be light and helps you stretch your PMC.

Soap

A simple way to get started is to carve a pattern into a bar of soap. Press PMC into the depression, peel it away, and you have a molded form. If you don't like the result, rework the carving and try again. Need a dozen? It's a simple matter of repetition.

Rubber Molds

Hobby shops sell a variety of molds intended for candy, candles and plaster. All will work for PMC, as will the cookie and butter molds you'll find at the kithen supply store. To make your own molds, buy a two-part silicone mold compound (like Rio Grande's Belicold, item #XXX-XXX). Most molds do not need lubrication but if the PMC sticks, spray lightly with cooking oil (eg. PAM).

Hollow Objects

Beads and other hollow forms are easy to make with PMC. Start by making a core from a material that will burn away completely. Examples include paper clay, Styrofoam, tissue, bread and cereals. Coat these with PMC, decorate and fire. In some cases the cores will send off smoke that you will want to vent.

Firing Tools

PMC can be fired in any device that will sustain the required temperature for the recommended time. These range from inexpensive torches and furnaces that need constant attention to programmable kilns that are fully automatic. When done correctly, all these devices will yield an equally strong result. Beyond reliability and convenience there is no reason to prefer one method over another.

Kilns

Small electric kilns are ideal and can also be used for glass, ceramics and burn out. A programmable unit allows you to set the ramp (heating up time), the holding temperature and the length of time the kiln will hold the desired temperature. Large ceramic kilns are not recommended because they usually have too much flucuation in heat from one area to another.

Torches

It is possible to fire PMC+ and PMC3 with any torch customarily used for jewelry work. Set the work on a soldering block in a dimly lit space and heat until the PMC glows red. Hold at a clear red for the prescribed time. A butane torch with a special nozzle reduces the risk of overheating.

Other Firing Arrangements

The introduction of PMC3 opens the door to a wide range of firing devices such as hot air guns, pellet (solid alcohol/Sterno) furnaces and some camp stoves.

500° F (260° C) Binder burns up, some flame, smoke and odor.

1000° F (538° C) PMC starts to show dim red glow.

1100° F (593° C) Clear red color; threshold for early sintering.

1200° F (650° C) Glowing red color, hold PMC3 here for 20 minutes.

1300° F (700° C) Bright red color, hold at this temp. for 10 minutes.

1400° F (760° C) Luminous, vibrant red color.

1500° F (815° C) Brilliant red/orange color.

1600° F (870° C) Glowing red/orange color; surface shimmers.

1700° F (926° C) Surface shimmers and appears wet.

1761° F (960°C) Surface shines like mercury, edges curl and the silver will draw up into a ball. Do not get to this point.

Firing Scenarios

For all types of PMC, allow the completed work to dry before firing. There is no problem with allowing PMC to dry Some natural stones may survive a PMC firing, particularly the low temperatures of PMC3, but there is always a risk that they will discolor or crack. Laboratory-grown gems, however, are created at very high temperatures and will always survive any of the firing scenarios shown on the preceding page.

Original PMC

1650° F (900° C) for two hours

PMC+

1650° F (900° C) for 10 minutes, or
1560° F (850° C) for 20 minutes, or
1470° F (800° C) for 30 minutes

PMC3

1290° F (700° C) for 10 minutes
1200° F (650° C) for 20 minutes
1110° F (600° C) for 30 minutes

Work can be allowed to air cool after firing or it can be quenched in water (as long as there are no stones or glass embedded in the piece). In all PMC the results after firing ar 100% pure metal. Work can be marked as Ag .999 or F/S for silver and 24K or Au .999 for gold.

Adding Gemstones

Some natural stones may survive a PMC firing, particularly the low temperatures of PMC3, but there is always a risk that they will discolor or crack. Laboratory-grown gems, however, are created at very high temperatures and will always survive any of the firing scenarios shown on the preceding page.

To Set a Small Faceted Stone

1. Prepare a seat or rim that will provide enough metal to surround the gem. This can be added to a form or built into the original shape.

2. Make a conical hole with a pencil point or similar tool.

3. Use a straw or similar tool to remove clay from beneath the stone.

4. Set the gem in position and press it down until the table is below the surface of the work. Remember that the clay around and under the stone will be contracting and will squeeze the stone upward. To compensate for this, press the stone deeply into the clay.

5. Fire as usual; air cool.

To Set a Flat-backed Stone

1. Create the object so that there is a smooth flat area for the stone.

2. Roll out a rod then flatten it to make a thick strap. Wrap this loosely around the stone then use PMC paste to join it securely to the base. If needed this can be scraped smooth when dry.

3. For large stones, make a "pie crust" cut in the back to allow the PMC to shrink without tearing.

To Set a Heat Sensitive Stone

A. Photocopy the stone with enlargement of 12% or 28% depending on the version you are using. Make a bezel around this shape and attach as above.

B. Wrap tape or polymer clay around the stone to make it larger, then press PMC over this to make a bezel that will be the correct size after firing. Remove the stone and attach as above.

Finishing

After firing, silver PMC has a characteristic matte white color. Because the surface has a microscopic texture, the effect is like there is a powdery skin on the silver. Press it even lightly and you will see how the texture gives way to a reflective silvery shine. As you might infer from this, some form of burnishing should always be part of the finishing process.	

Hand Burnishing

Perhaps the most basic (and rewarding) way to polish PMC is to rub it with any hard smooth object. Commercial burnishers offer a time-tested shape in a comfortable handle, but you can use knitting needles, teaspoons and polished nails. Lubricate the action with a few drops of water and rub the PMC in all directions to make it shine. Follow this with a polishing cloth to remove burnishing marks.

Polishing Papers

Exciting developments in the last decade have given us a huge new selection of abrasive papers that not only cut faster but also leave a brighter shine than was possible with papers before. Move systematically from coarse to fine grits, changing directions with each switch. For increased leverage, wrap the papers around a tongue depressor or similar support.

Scratchbrushing

Brushes made from very thin brass or stainless steel wires can be used to burnish PMC. Lubricate with any sort of soap and work under a slow drizzle of water. Scrub in all directions. This can be used in conjuction with any other technique.

Tumbling

A tumbler is a mechanical device in which hundreds of steel balls and rods cascade against jewelry objects as they rotate in a drum like a miniature clothes dryer. The advantages are that many pieces can be done at once and that individual handling is minimal. For this reason tumbling is often the choice of production artists.

Combining with Other Materials

Whole books can be written about the wealth of opportunities that exist to combine silver or gold PMC with glass, polymer, paper, leather, fabric, shells, found objects, enamels, wood &ldots; well, you get the idea.

Polymer Clay

Make a PMC object and fire it as usual. Sand, burnish and complete any soldering, then press polymer clay elements into it. If possible, provide handles of silver to grip the polymer. Cure the polymer at its recommended temperature (see package, manufacturers differ). This will cause no harm to the fired PMC. In some cases it is recommended to glue the polymer to the PMC.

Glass

PMC can be used with glass in many creative ways. There are many formulations of glass with a wide range of melting points. Expermentation is recommended. Completed PMC objects can be inserted into lampworked or blown glass, and glass can be slumped over it. Silver has a tendency to create a green tint in some glass. To reduce stresses, all glass should be cooled slowly in a process called "annealing."

Enamels

PMC is made for enameling! Create a silver object with recesses, fire and finish as usual. Wash enamel powders and pack them into the recesses. Dry and heat (torch or kiln) until the powders melt and fuse. Repeat as needed to fill the cavity.

It is also possible to mix enamel powders into PMC to create a metal/glass hybrid. Knead equal parts together, model a form and fire for a slightly shorter time than usual.

Found Objects

PMC can be used with brass, steel and nickel silver elements, though because of heavy oxidation the PMC will not fuse to base metals. Plan ahead to create a mechanical connection like a hook, prong, rivet or undercut to secure the pieces together.

Health & Safety

Totally Non-Toxic

Precious Metal Clay has been certified by an independent testing facility to be safe in every phase of its use and to confirm to ASTM D4236. Issues of safety arise not from PMC, but in the normal use of the high temperature furnaces used in the sintering process. These kilns should be positioned on a stable surface, away from combustible materials. Never leaeve a kiln unattended and take special care if animals or young children are in the area. As always, when working around heat, wear appropriate clothing, avoiding clothes made of synthetic fabrics. There is little reason to stare into a kiln but if you need to do this, proteactive lenses should be worn. (see your Rio Grande Tools and Equipment catalog).

Storage and Shelf Life

You'll notice that Precious Metal Clay is packed in an air-tight foil pouch to preserve its freshness. Use this pack or a good quality plastic wrap (or both) to keep the clay moist. It is good practice to take out only what you can use in a few minutes and to add a few drops of water to the lump at the end of each work session.

All three versions of PMC can be rehydrated if they dry out, though it is difficult to achieve the homogenous consistency of fresh PMC. To restore dried material, poke the lump with holes or dice it into small pieces. Add water by kneading, then set the PMC aside to allow the water to penetrate. Allow at least a day, more if the clay was very dry. With the sample wrapped in plastic, knead repeatedly to force the water into the dense metal structure. If you accidentally add too much water, spread the PMC on a piece of plastic, glass or waxed paper and allow it to dry to a usable consistency.

For more information, contact Rio Grande 7500 Bluewater Rd. NW, Albuquerque, NM 87121 USA 505/839-3000 Toll free: 800/545-6566 info@riogrande.com

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