Metal Clay Shrinkage Calculators
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You can create your own metal clay (also known as “lump” metal clay), paste, slip, or oil paste. You can also add ingredients to your metal clay to modify its properties; or to make it better suited for a particular use. This page contains information about metal clay ingredients and links to metal clay recipes.
Metal clays made from the same metal (such as silver) can usually be used together to make one piece. The piece should be fired at the highest temperature required for any of the mixed clays. If the clays have different shrinkage rates, the piece may warp when it is fired.
Some types of metal clay contain different ingredients than others, and while most of these can still be used together in one piece (so they are touching), some should not be mixed together to make a single lump of clay or clay paste.
This is the typical, common type of metal clay. It is the thickest kind, and looks and feels like a lump of clay.
The terms “slip” and “paste” can be used interchangeably. Paste is a more liquid version of metal clay. Paste is used to add details or texture, or to attach greenGreen pieces have not been fired. metal clay pieces together. The metal clay pieces may be wet or dry. You can make your own paste from metal clay.
To create paste, add a small amount of water to the metal clay. You can also add a bit of vinegar to prevent mold. Note that bronze paste can eventually separate with the tin rising to the top, creating a dark surface layer; this should be stirred in.
Note: This is not the same as oil paste.
It is difficult to make your own paste syringe. The paste can be mixed as usual, though it will require some experimentation to find the best consistency. The paste should be mixed as thoroughly as possible, so it is all of the same consistency. One difficulty lies in filling the syringe with the metal clay paste, without creating air bubbles. Note that the syringe should not have any metal parts that touch the clay, unless you know that the metal will not react with the clay.
This is often called “Lavender Oil Paste.” Oil paste is used to attach metal clay pieces that have already been fired, or to repair broken or cracked fired pieces. You can make your own oil paste from homemade or purchased metal clay.
Note: Do not use Art Clay Oil Paste on unfired clay, or mix Art Clay Oil Paste with
unfired metal clay or paste.
It contains a different kind of binder that is incompatible with unfired clay.
Homemade oil paste is compatible with unfired metal clay.
Most people use lavender oil to make oil paste. However, other essential oils can be used. Olive oil works; some have tried citrus (orange, lemon, tangerine) and peppermint. Apparently tea tree oil doesn't work as well as lavender.
To make lavender oil paste, add a few drops of tincture of lavender oil (which contains essential oil, alcohol, and water) to metal clay. If you have pure essential oil, which is more concentrated, use less oil and add water or alcohol. You want to create a thick, spreadable paste. A little glycerin may help make it creamy; a little rubbing alcohol can make it more workable. After mixing, let it sit overnight. Add a little distilled water if the paste is too thick.
The PMC Guild has instructions to Make Your Own Metal Paste.
Metal clay is also available as a sheet or paper. This is thin and flexible metal clay. Since it is thin and delicate, it is often used to add pieces to other metal clay. It can also be used for origami or woven pieces. Pieces made only from sheet clay cannot be fired with a torch.
Do not add water to metal clay sheet; it will fall apart. You can use a small amount of water to glue the sheet to a piece of metal clay.
Purchased metal clay sheet uses a different type of binder than the lump clay, and should not be mixed with regular clay.
Note: Metal clay paper is a variety of metal clay. Paper clay is an entirely different clay made of paper, not metal.
These are some of the ingredients that can be used to make metal clay or additives that can be mixed into packaged metal clay. Some of these ingredients may not be readily available in your area. Generally only natural or organic ingredients should be added to metal clay, or used on your hands when working with the clay. Artificial ingredients can affect the workability of the clay and may not burn out when the clay is fired.
Some metals are much stronger than others. The stronger metals will be more forgiving of less-than-ideal mixtures, since weak metal clay will still be strong enough for most purposes. Adding ingredients to metal clay may also affect its shrinkage rate.
Do not use tap water. Water from the tap (from a city water supply or well) contains minerals that may interact with other ingredients in the metal clay and interfere with sinteringSintering makes a solid object by heating powder without melting.. Use distilled water or deionized water with your metal clay.
When making your own metal clay or mixing from metal clay powders, the water should be sprayed onto the powder. Add the water gradually. After the clay starts forming lumps, the clay can be mixed together. If you add too much water, you can spread it out and let some of the water evaporate.
Many people add olive oil to metal clay. The oil slows drying and improves the workability of the clay. Other oils may work as well. Do not add too much oil to the clay; it makes the clay unworkable and unusable. Too much oil may also reduce the strength of the finished piece.
Lavender oil is often used to make “oil paste” for fixing fired pieces that are broken or have cracks. Oil paste is also used to attach fired pieces to each other. The lavender oil smells nice, but other essential oils can also be used.
There are reports that lavender oil slows oxidationOxidization is a chemical reaction combining the metal with oxygen from the air, like rust (iron oxide). of copper and bronze metal clays.
Glycerin can be produced from plants or animal fat. Vegetable source glycerin is safe to eat.
Glycerin makes the clay more workable, and slows the drying time. If you add enough glycerin, the metal clay will remain flexible even when dry. Adding too much glycerin may reduce the strength of the finished piece.
After clay has been mixed or opened, a few drops of vinegar will prevent it from developing mold.
Metal powder used to make metal clay should contain very small particles—no larger than 20 microns in size. Many commercial metal clays have particles between 1 and 20 microns. The size of the metal particles affects the firing temperature and time, as well as the strength of the finished piece. Different sizes of particles may be combined—this helps fill some of the empty spaces between the particles.
The metal particles may be spherical (round) or flakes. Flakes may make the clay softer and easier to work with, but reduce the strength. The original Silver PMC uses flakes.
CMC powder is a cellulose product used as a binder. Cellulose is obtained from green plants, such as wood pulp or cotton, and is the main ingredient in cardboard and paper. CMC is available from pottery or bakery stores. Other cellulose powders would probably work as well.
This is one brand of CMC.
Polyolefin powder is not a natural product, it is synthetic. It is used for car covers and seat cushions. Polyolefin burns relatively cleanly, and produces heat at a fast rate. This may help with sintering.
Note: Most commercially available metal clays use only organic ingredients for binder.
Starch can be used as a binder. Cornstarch (also called corn flour in some countries) and wheat flour can be used to make metal clay. Besides cornstarch and regular flour, you might experiment with rice starch and potato starch. The ideal binder is finely ground so that it has small particles, and burns relatively cleanly.
Wax, gum, agar, resin, and propylene glycol have also been mentioned as possible ingredients for metal clay.
Petroleum jelly and mineral oil are not recommended. Petroleum can degrade the binder. Do not use a petroleum-based product on your hands before working with clay.
Making your own metal clay is certainly more difficult than buying ready-made clay or clay powder, and requires dedicated equipment. Some of the ingredients may have to be purchased in large quantities. Note that even non-toxic ingredients can be dangerous if not handled properly—consider buying metal clay powder instead of trying to make your own.
These recipes were created from experimentation. It is likely they contain different ingredients than metal clays that can be purchased. Because of this, the properties of homemade metal clay will probably differ from the commercially available versions. Note that the commercial versions have been extensively researched and tested, and will likely produce more consistent results than do-it-yourself (DIY) metal clay.
The workability and drying rate of the clay depend on the ingredients and mixing process. You can fabricate metal clay in an aerosol mixer or a household blender. Metal clay should be easily worked when wet, easily carved when dry, and strong when fired. To create a strong metal clay:
A bad batch of homemade metal clay may not sinterSintering makes a solid object by heating powder without melting. properly. If it does sinter, it may not be very strong. You may have to experiment with different ingredients and firing schedules for your homemade metal clay. Firing hotter and longer will make stronger clay, but you must stay below the melting point of the metal.
Follow proper safety procedures. Though the ingredients used in metal clay may be non-toxic, the powders can be dangerous to inhale.
In the United States, Material Safety Data Sheets (MSDS) contain information on the safety of various substances. These are available in other countries as well; MSDSs are country-specific. Check the MSDSs of any unknown ingredients before purchase. Note that products from different suppliers may contain different ingredients and have different MSDSs.
If you use any ingredients that are not organic, be sure you know what chemicals are produced when they are burned. Never breathe the fumes produced when firing any metal clay, even if all ingredients are organic.
The percentage of metal clay shrinkage depends on the size of the metal particles and the particles in the binder, and the amount of binder in the clay. If you are using ingredients from your kitchen, the particle sizes are unknown; and may vary from one batch to another. You may not get consistent results when making your own metal clay.
The order of mixing can make a difference in the success of your metal clay. This is the recommended order:
All of these metal clay recipes can probably be modified for bronze, copper, silver, or gold clay.
Bronze is an alloyAn alloy is a mixture of a metal with one or more metals or nonmetals. of copper and one or more metals, usually tin. Only make as much bronze clay as you plan to use. The bronze clay will begin to oxidizeOxidization is a chemical reaction combining the metal with oxygen from the air, like rust (iron oxide). when it is exposed to air.
A recipe for bronze clay from Del Feast may be found at Metal Clay Academy: Make Your Own Metal Clay. It uses easily available ingredients, but after it has been fired it may not be as strong as the commercial versions of clay. Don't try to make thin pieces from this clay until you have tested its strength.
Note: Follow proper safety procedures. When working with these powders, you must wear the correct dust mask. Items used for making the metal clay should not be used for food.
These are the ingredients used for a “kitchen” version of do-it-yourself bronze clay:
Bronze powder contains mostly copper. The remaining ingredients are natural/organic, so will burn out when the clay is fired.
Other, similar ingredients will also work—he has also experimented with rice starch instead of wheat, with excellent results. Make sure than all ingredients have a small particle size.
A silver clay recipe may be found at the Rings & Things Community Forum: Making Silver Clay. Metal clays using other metals (such as gold or copper) can probably use a similar recipe and process.
Note: Follow proper safety procedures. When working with these powders, you must wear the correct dust mask. Items used for making the metal clay, such as a blender, should not be used for food.
Three lab techs (who make and test specialty paint) experimented to create a recipe for silver metal clay. This is a list of the ingredients:
The humidity in your area will affect how much liquid you need to add to the clay.