I believe the balls you are showing are made of "Ivorene" as it was called, made by Aramith, a Belgian manufacturer. It is a phenolic resin based ball, not real ivory. I have many sets of billiard balls from the century old Brunswick Billiard Tables I have collected and are available for the public to experience at Rack & Roll Billiard Hall and Museum. I have gathered information from reliable sources and copied the information here:
The first billiard balls were ivory. With an elephant tusk just three or four balls could be produced in a long process, so they ended up being very costly. The high price coupled with the fragility and little homogeneity of the balls made that way thus forced to seek a more affordable material.
An American inventor, John Hyatt, found in 1860 a great substitute for ivory: nitrocellulose. Mixing it with alcohol, a plastic material to manufacture much cheaper balls was achieved. The problem was that the material was like wildfire and a strong hit could make it explode.
Half a century later, the chemist Leo Baekeland invented bakelite, the type of phenolic resin with which most of billiard balls are manufactured today (though it is also used for its great advantages: it is very resistant to heat, it is cheaper and it allows getting perfectly spherical, highly impact resistant and less dirty balls).
Aramith... A Legend in the Billiard World
For several decades Belgian Aramith Billiard balls have enjoyed a legendary reputation for outstanding endurance and uncompromising quality. Made by Saluc in Belguim, Aramith excellence is the result of a high-tech process that combines the unmatched characteristics of phenolic resin with fine Belgian craftsmanship. Aramith's consistantly reliable performance guarantees players the pleasure of razor-sharp precision. Their exceptionally long product life offers the table owner the best value for the buck year after year!
Aramith phenolic resin : why it makes the difference!
Heavy duty design
Rather than a polyester number-plug-design, the Aramith concept has the numbers precision-engraved in a solid core that runs all the way through the ball. As such, it is impossible for number-cores to fall out over time. Using phenolic resin assures homogeneous characteristics in each ball part. So homogeneous that when finally getting to its breaking point (and one needs minimum a 5 ton-load in case of an Aramith ball), the ball will break up totally at random, and not along the parting line between the stripe and the rest of the ball, as one would expect.
Hitting a cue ball actually accelerates it from 0 to over 30 km/h (20 MPH) in just a fraction of a second.The resulting friction temperature between ball and cloth can easily reach 250°c (482°F). That’s why Aramith balls are the only ones made from genuine phenolic resin : their molecular structure is engineered to be wear resistant at these high temperatures, making Aramith balls far less vulnerable to abrasive burn-spots. They hold their high luster and smoothness over a much longer period of time, resulting in minimal ball and table cloth wear.
High Impact resistance
Because hitting the balls is the essence of the billiard game, impact resistance is a critical factor. Aramith’s phenolic heat-curing process fully stabilizes material tensions. It produces a vitrified high-density surface that offers maximum impact resistance. Tests show Aramith phenolic balls to withstand to over 50 times more impacts than other polymer or polyester balls. They are also twice more scratch-resistant. Consequently, when intensively used even on less maintained tables, Aramith balls are clearly far less easily damaged than others by pocket fixings, table mechanisms or cue sticks…