This family has apparently been doing a lot of things right from a business and operations management perspective. But their alloys are not "secret". It's actually never been a secret :) Production of cymbals is one of the lesser-known deep-rooted traditions in Istanbul.

http://www.aa.com.tr/en/culture-and-art/468267--holy-metal-i...

FWIW "Zildjian" is a mix of Turkish and Armenian. "Zilciyan" would be the Turkish spelling where "Zil" is cymbal or bell in Turkish, the -ci suffix adds a "seller-of" or "manufacturer-of" meaning and -yan == -ian, "descendant-of" in Armenian.