585 chain with 3 hallmarks
This is gold-plated material on a silver base. The 585 stamp matches the gold plating. Therefore, an acid test is unfortunately not sufficient.
What is striking here is once again the design of the clasps and the weight of the jewelry.
In the pictures you can clearly see that the clasps are offset from each other; this is usually not the case with high-quality gold jewelry, as this impairs the wearing comfort.
Furthermore, the locking ring is open. It can easily come loose and is usually soldered. This is not the case here.
Last but not least, the chain is hallmarked three times: on the clasps and on the clasp ring. This is more than unusual.