Today, virtually all petanque balls are made from some kind of steel.
Steel (in French, acier) is a carbon-iron alloy. The ratio of carbon to steel in the alloy has a significant (and rather complex) influence on the properties of steel. Different kinds of steel may also contain other metals, such as nickle and chromium.
Twenty different steels are used by different manufacturers of boules. In addition to the composition of the steel, different heat treatments (tempering) can give each kind of steel its own properties — corrosion resistance, stress resistance (modulus of elasticity, yield strength, mechanical strength), hardness, and impact strength (resilience).
The two major types of steel used in boules are carbon steel and stainless steel.
Note that a boule’s hardness is determined by the way that it is heat-treated (tempered), NOT by the material that it is made of. You can make a hard or a soft boule from both carbon steel and stainless steel.
Carbon Steel (acier au carbone)
Carbon steel boules provides excellent grip in the hand and on the ground. Carbon steel, unlike stainless steel, can rust, but this is not a serious issue. Regular play will scour away rust. If you are putting them away for a while, a light coating of talcum power, oil, or WD-40 will keep them from rusting while in storage.
Stainless Steel (acier inoxydable, or simply inox)
Stainless steel is an alloy containing (in addition to iron and carbon) nickel and chromium. Stainless steel gives a smooth, satin feeling that generally facilitates the release of the ball. Stainless steel balls require no special maintenance, and a simple cleaning with soap and water is enough to restore the balls’ shine. Stainless steel boules are more expensive than carbon steel boules. OBUT uses the star symbol ★ to designate an inox boule.
Bronze and aluminum
The first all-metal boules were made in about 1925, by Le Boule Integral. They were cast in a single piece from a rather soft alloy of bronze and aluminum. Integral no longer exists, but there are a couple of companies that still make the original bronze/aluminum boules. Since they are not made of an iron-based alloy they will not rust and they cannot be picked up by a magnetic boule-lifter. These boules have a bright gold/brass color. They are real shooter’s boules, they look great, and they are expensive.
At one time Integral also made leisure boules with a dull grey finish that looked more like aluminum than brass. Every now and then an old pair turns up on eBay. You can tell that they are Integral boules because they, too, are non-magnetic.
How is a boule made?
There are two main ways to make a metal boule. The first is to mold the the entire ball as a single, complete spherical object. That is how the old Integral boules were made.
The other method is the one that is used by every modern boule manufacturer. Steel rods are cut into blobs of steel, and the blobs are mashed down into round disks. The disks are stamped into the shape of hollow hemispheres (coquilles, shells). Then the hemispheres are welded together to create a hollow sphere. The sphere is then machined on a lathe to give it a nice smooth surface, and grooves. Then information about the manufacturer’s model number, the weight, etc. are stamped or cut into the boule’s surface. At some point the boules are tempered — reheated and slowly cooled again to give them the desired hardness. (Youtube video of boules being made)
What material should I choose when buying a competition boule? ▲
When it comes to material, there are two basic choices: carbon steel and stainless steel (inox), although within those two broad categories there are many slightly different types of alloy. The old “bronze” (copper-aluminum alloy) Boule Integral is still available, but it is a good choice only for very advanced shooters.
Carbon steel balls may come in a variety of surface colors — chrome, red, blue, black, La Boule Bleue, La Boule Noire — but those colors are just a thin layer of paint to keep the boule from rusting while it sits on the self. The paint will quickly wear off during use (an afternoon of play is often enough to do the job) leaving a surface of bare metal. Depending on the precise type and hardness (determined by the tempering) of the steel, the exposed surface may vary from a rough matte black to a surprisingly smooth and shiny silver.
Some players feel that stainless steel gives a smooth, satiny feeling in the hand that facilitates the release of the ball, while carbon steel provides more “grab” in the hand and on the ground. If this is true, then a pointer may prefer a carbon ball, while a shooter may prefer a stainless steel ball.
That “grab” or roughness is a consequence of the fact that carbon steel boules (unlike stainless steel boules) will rust. In the presence of heat and humidity, microscopic areas of rust (iron oxide) form on the surface of the boule and then flake off, leaving the microscopically rough and pitted surface that gives a carbon steel ball its “grab”.
Rust is not an issue if you play with your boules regularly. If you are putting them away for some time in storage, packing them in rice, or dusting them with baby power or talcum powder, or wiping them with a bit of oil or WD-40, will keep away rust.
And even if your boules rust, it is not a disaster. Just playing with them for a few days will abrade away the rust. In a worst-case scenario, a scrubbing with a wire brush in a bucket of water can usually transform an ugly ball of orange rust into a wonderful glowing dark boule with a lot of character.