Pick The Best Metal Clay Formula For Your Project

The two major brands of precious metal clay are PMC (made by Mitsubishi Materials Corporation of Japan) and Art Clay (made by Aida Chemical Industries Ltd.).  To a large extent, the choice is one of personal preference - like Coke vs. Pepsi. However, there are some significant differences that may affect your choice for a specific project.

For example, PMC Standard (AKA Original PMC) is the only metal clay that shrinks 25-30% after drying and firing. This can be a very useful characteristic in certain situations (see Shrinkage, below). And Art Clay offers certain types of products that have no equivalent in the PMC brand.

Here are some important considerations in choosing the best clay formula for a specific project.

Shrinkage

Different brands and formulas of metal clay have different amounts of binder and water, and therefore have different shrinkage rates after drying and firing.

• PMC Standard (AKA Original PMC)  25-30%
• PMC+  10-15%
• PMC3  10-15%
• PMC Gold (22K)  14-19%
• Art Clay Silver - Standard  8-10%
• Art Clay Silver 650/1200 (Low Fire)  8-9%
• Art Clay Gold  15%

For some types of projects, you may want the 25-30% shrinkage that only PMC Standard (AKA Original PMC) provides. For example, if you want to make a matching pendant and earrings from a mold, you might want to make the pendant out of lower-shrinkage clay and make the earrings out of PMC Standard so that they will be smaller versions of the pendant.

Another reason to choose the higher-shrinkage PMC Standard is when you want to create a curved surface. By adhering a layer of lower-shrinkage clay on top of a higher-shrinkage clay, the different shrinkage rates will create a convex curve.

Lastly, the high shrinkage rate of PMC Standard can be an advantage when you are adding a lot of detail because you can work "larger." The details will be sharper and crisper after firing.

Strength

PMC Standard is not as strong as other metal clay formulas, so it isn't suitable for items like rings that will be subject to a lot of wear and tear. But for a pendant, it's just fine. PMC3 is a little stronger than PMC+ and so is more suitable for rings, but either can be used. I have not found relative strength comparisons of the Art Clay formulas, but the Low-Fire formulas are denser and, therefore, presumably stronger than the Standard formula.

Firing Time / Temperature

In general, you get the best strength from firing at the hottest allowable temperature for the longest allowable time.

But sometimes, you want a clay that can be fired quickly (for example, if you want to torch-fire it) or one that can be fired at a lower temperature (for example, if you are embedding sterling silver findings, glass, or certain heat-tolerant gemstones).  

For a giving formula of clay, the lower the firing temperature, the longer the firing time required.

Low-Fire Clays

• PMC3 can be fired at 1290ºF for 10 min., 1200ºF for 20 min., or as low as 1110ºF for 30 min.
• Art Clay Silver 650 can be fired at 1472ºF (or up to 1650ºF) for 5 min., 1380ºF for 10 min., 1290ºF for 15 min., or as low as 1200ºF for 30 min.

Medium-Fire Clays

• PMC+ can be fired at 1650ºF for 10 min., 1560ºF for 20 min., or as low as 1470ºF for 30 min.
• Art Clay Silver - Standard can be fired at 1600ºF-1650ºF for 10 min., 1560ºF for 20 min., or as low as 1472ºF for 30 min.

High-Fire Clays

• PMC Standard/Original must be fired at 1650ºF for 2 hours.

Gold Clays

• PMC Gold (22K) can be fired at 1650ºF for 10 min., 1560ºF for 30 min., 1380ºF for 60 min., or as low as 1290ºF for 90 min.
• Art Clay Gold must be fired at 1814ºF for 60 min.

Working Time

Art Clay offers two slow-dry formulas that give you significantly more working time if you are creating a complex design or are working in a very dry environment.

Art Clay Silver - Slow Dry formula dries out much more slowly than the Standard formula, allowing you about five times more working time.

Art Clay Silver 650 - Low Fire/ Slow Dry formula gives you four times more working time than the Standard formula, but it can be fired as low as 1200ºF, which provides lots of advantages if you want to embed sterling silver findings, glass or certain heat-tolerant gemstones.

Oil Paste and Overlay Paste

Art Clay makes two specialty paste products that don't have equivalents in PMC.

Art Clay Silver - Oil Paste is an oil-based silver clay product that creates a very strong bond when joining pieces of fine silver (such as joining already-fired metal clay or attaching fine silver wire or findings to fired metal clay).

Art Clay Silver - Overlay Paste is a paste form of Art Clay Low Fire clay that can be used to add fine silver accents to glazed porcelain, ceramics or glass.

Lump, Paste, Syringe or Paper

Depending on your project, you may need/want to use a specific type of clay, e.g., lump, paper, syringe, paste. Not all formulas come in all types. (For example, PMC Standard/Original comes only as lump clay. You need to mix your own paste, and there is no syringe.) PMC Paper is PMC+.  Art Clay Silver - Paper Type is  Art Clay Silver - Standard comes as lump clay and paste, but not syringe.

You can mix different formulas of clay as long as you fire at the longest time/highest temperature required by any of the formulas you are using. So, for example, if you are using PMC+ woven paper strips attached to a base of PMC Standard/Original clay so that it will curve during firing, you must fire at 1650ºF for 2 hours (because although PMC+ can be fired shorter/cooler, PMC Standard cannot).

One Size Doesn't Fit All

PMC+ and Art Clay 650 (Low Fire) are strong, versatile metal clay products that can be the workhorses of your metal clay toolkit. But clearly, there are many situations in which other formulas will be better suited to a particular project or application. These guidelines should help you make good choices for your specific needs.