I had someone contact me about a week ago, trying to date these Zildjian cymbals. Based on the description they sent me, here was my response ...
The name "Constantinople" was changed to "Istanbul" in 1930, so that means your cymbal is older than 70 years ... UNLESS ... the cymbal is actually stamped "A Zildjian & Co. Genuine Constantinople Cymbals", which was used on a few models in the late 1970's. The letter "A" in the stamp proves that the cymbals were not made in Turkey, which is where the K Zildjian factory was.
If your cymbal says "Made In Turkey" and just says "Zildjian & Co." and "Constantinople", I am 99.9% sure that your cymbal was made prior to 1930. To be exact, however, I'd have to see the cymbals ... but even then I don't know that I would be able to do any better.
Well ... they sent me a few photos, close up shots of the logo ... and I'm not thinking these are pre-1930's but rather 1970's cymbals.
The lathing doesn't look right to be a pre-30's; and I own a pre-30's Zildjian. The stamp isn't what I thought it was from his original description. I don't know that I've seen these kind of stamps before.
Any thoughts?