What is Anticlastic Jewelry?
Anticlastic jewelry is a series of techniques used in metal forming to create handcrafted jewelry. The artist stretches sheet metal to create a concave curve on the outer surface while compressing the metal to create a convex curve in the middle. Both major curves, which are at 90 degrees to one another, go in the same direction. The bowl or dome shape is the ultimate form. Anticlastic jewelry is very unique and requires great patience and skills from the jewelry designer.
Key Takeaways
- Anticlastic raising shapes flat metal into a saddle form, like a Pringle chip.
- The edges are stretched and the center is compressed. The two curves sit at 90 degrees.
- Hammering work-hardens the metal. Copper can become about 55% stronger.
- The double curve adds stiffness, so thinner and lighter sheet can be used.
- Silver, gold, copper, bronze and aluminum all work well.
- The technique dates to Bronze Age Ireland and returned in the late 20th century.
Anticlastic Jewelry by the Numbers
According to the Copper Development Association, hammering raises copper's tensile strength from about 32 ksi to about 50 ksi, making it roughly 55% stronger.[1]
Data from The Aluminum Association shows that aluminum weighs about one-third as much as steel, making it roughly 66% lighter for the same size piece.[2]
According to the U.S. Geological Survey (USGS), aluminum makes up about 8% of the Earth's crust by weight, more than any other metal.[3]
Research cited by the Copper Development Association shows that about 80% of all copper ever mined is still in use today.[1]
Data from The Aluminum Association shows that recycling aluminum uses about 95% less energy than producing new aluminum.[2]
Under the U.S. FTC Jewelry Guides, sterling silver must contain at least 92.5% silver, and 14K gold must contain 58.3% gold.[4]
According to the Copper Development Association, bronze is traditionally about 88% copper and 12% tin, the same alloy used in Bronze Age metalwork.[1]
The Process of Anticlastic Raising
During the process of anticlastic rising, a flat sheet of metal is formed by stretching the center and compressing the sides so that the metal creates two curves that are of right angles to one another. While the pattern of the sheet is important to create the desired form, various forms can often be made from the same pattern. The final result is that of a “Pringle” potato chip or saddle shape.
Anticlastic raising is generally performed with a combination of plastic, steel, and wooden tools. A steel stake and plastic mallet are usually the quickest technique, but offers less control which ultimately requires more planishing. The preferred method is typically a plastic stake and steel hammer. This combination requires minimal planishing, and offers good speed and control. Available in various shapes and sizes, the stakes used in anticlastic raising primarily depend on the width of the metal and desired curves. The width of the pattern cannot exceed the distance between the crests.
Metals Used in Anticlastic Jewelry
Anticlastic raising is best suited for ductile metals, including silver, gold, copper, and bronzes. When this technique is used for jewelry, the metal can be quite thin. Shoppers can find a large selection of anticlastic jewelry as the technique offers a unique variety of design choices. Some popular choices include anticlastic earrings, cuffs, and bracelets. These pieces of art are highly sleek, sensual, and contemporary with a handcrafted touch.
Due to today’s high metal prices, a major advantage to anticlastic raising is the ability to create relatively thin and structural strength forms. The result is often a form that is springy and flexible, such as a necklace that requires flexibility to be worn comfortably. Anticlastic raising is both modern and ancient, with little history in between. During the Bronze Age Ireland, a ribbon torc necklace was crafted from a sheet of metal and twisted into a double helix. This creative technique of metalworking did not appear again until the end of the 20th century.
What Does the Research Say About Anticlastic Forming?
Anticlastic forming is backed by clear metal science. Here are the key facts.
Modern anticlastic raising was developed by Finnish-American metalsmith Heikki Seppä. His book Form Emphasis for Metalsmiths, published by Kent State University Press in 1978, set out the technique for jewelers.[5]
Hammering makes metal stronger. According to the Copper Development Association, pure copper has a tensile strength of about 32 ksi when soft. When fully hard-worked, it reaches about 50 ksi. That is roughly 55% stronger.[1]
Data from the Copper Development Association puts copper's density at about 8.96 g/cm³. Bronze is about 88% copper and 12% tin.[1]
According to The Aluminum Association, aluminum's density is about 2.7 g/cm³. That is roughly 70% lighter than copper.[2]
Under the U.S. FTC Jewelry Guides, sterling silver must be at least 92.5% silver. 14K gold must be 58.3% gold.[4]
The saddle shape is also used in architecture. Engineers call it a hyperbolic paraboloid. It is prized because a thin shell can span a large area while staying rigid.[6]
How Much Metal Does Anticlastic Forming Save?
I tested how much lighter a cuff can be when the anticlastic curve does the structural work. I ran a side-by-side calculation on a 6-inch, 1-inch-wide cuff blank. I compared thick flat sheet with the thinner sheet an anticlastic form allows.
| Sheet | Thickness | Weight in Aluminum | Weight in Copper |
|---|---|---|---|
| 16-gauge (flat cuff) | 1.29 mm | About 13.5 g | About 45 g |
| 20-gauge (anticlastic cuff) | 0.81 mm | About 8.5 g | About 28 g |
Switching from 16-gauge to 20-gauge sheet, the aluminum cuff's weight dropped from 13.5 g to 8.5 g. That is about 37% lighter. In copper, it dropped from 45 g to 28 g.
What Have We Learned Making Anticlastic Jewelry?
In our experience, the saddle curve is what lets thin metal feel solid. A flat strip of thin sheet bends easily. Raised into an anticlastic form, the same strip resists bending in both directions.
The Hammered Aluminum Anticlastic Bangle Bracelet shows this well. It is light enough to forget you are wearing it. Yet it holds its sculptural shape day after day.
Hammering adds a second layer of strength. Each blow work-hardens the surface. It also leaves facets that catch the light.
We use a plastic stake and steel hammer for most pieces. In our experience, that pairing needs the least planishing. It also keeps the curves smooth and even.
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Frequently Asked Questions
Q1. What is the difference between anticlastic and synclastic forming?
In anticlastic forming, the two main curves bend in opposite directions, creating a saddle shape. In synclastic forming, both curves bend the same way, creating a bowl or dome shape.
Q2. What metals work best for anticlastic jewelry?
Ductile metals work best. These include silver, gold, copper, bronze and aluminum. They stretch and compress without cracking.
Q3. Why are anticlastic cuffs strong even when they are thin?
The double curve resists bending in both directions. Hammering also work-hardens the metal. Together, they let thin sheet stay rigid and light.
Q4. Who developed modern anticlastic raising?
Finnish-American metalsmith Heikki Seppä developed the modern technique. His 1978 book, Form Emphasis for Metalsmiths, taught it to a new generation of jewelers.
Q5. Which John S. Brana pieces use anticlastic forming?
Examples include the Hammered Aluminum Anticlastic Bangle Bracelet and other anticlastic cuffs and bangles in aluminum, copper and bronze.
References
- Copper Development Association. Copper and copper alloy properties, recycling and applications. https://www.copper.org/
- The Aluminum Association. Aluminum properties, density and recycling data. https://www.aluminum.org/
- U.S. Geological Survey (USGS). Aluminum and mineral commodity information. https://www.usgs.gov/
- U.S. Federal Trade Commission. Guides for the Jewelry, Precious Metals, and Pewter Industries, 16 CFR Part 23. https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23
- Seppä, Heikki. Form Emphasis for Metalsmiths. Kent, Ohio: Kent State University Press, 1978.
- Encyclopaedia Britannica. Hyperbolic paraboloid and shell structures in architecture. https://www.britannica.com/
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