Zilko were first made of brass and then sometime after 1952 they were switched to NS12 - They were never made of B20.

They were later called "Standards" and "Zilko Standards."

Imo, the cymbals sold through Arbiter are mid-60s era when Arbiter-Western started and Ivor started importing instruments from other countries to the UK.

The Zilket looks like a 60s era cymbal as well. Have found no proof that they existed in the 1950s and were probably made special for Arbiter as they are not even listed on the Paiste 2009 corporate timeline.

Also because the OP's Zilkos are stamped Switzerland they are from 1957 onwards. The Swiss factory opened in 1957 so they can't be from 1956.

There is a chance these might be brass Zilkos, the NS12 Zilkos made in Switzerland at this time were possibly embossed as Standards.

I have tried getting clarification on the history of the Zilko line from Paiste Switzerland but even they are a little confused and say the names Zilko / Standard / Zilko Standard were used somewhat interchangeably.

It's possible that Zilko were always made of brass and the Standard / Zilko Standards are the NS12 cymbals.

The Arbiter Zilko were NS12 cymbals. Probably leftover or a continuation of Zilko Standard from earlier in the 60s but now for export only as according to Paiste the Zilko Standard line came to end as a Paiste product in 1963.

Drum Dad if you are still out there I would every much like to see this 1958 Paiste catalog you have. I have the 1950 and 1952 catalogs. Let's talk!

Okay coming back to this as I have found some more 50s Paiste catalogs and have some more thoughts on this topic.

Almost positive now all Paiste Zilko cymbals are indeed all made of brass and were made until 1959. It looks all Swiss Zilkos were made in 1957 only while the German factory made them for another year.

The Standard (also stamped as Zilko Standard) were made of NS12 and were made from 1958 (first in the Swiss factory) to about 1963 (and then probably replaced by the SUPER as the cheapest Paiste).

The Arbiter Zilko is either an OEM continuation of the Paiste Zilko Standard or perhaps the Arbiter version of the Ns12 Dixie.

The Zilket was a cheap student cymbal set (in very few sizes) It looks the Zilket was made strictly for Arbiter and is most likely akin to a Ns12 SUPER.

It looks Paiste first started exporting from Switzerland directly to the US and Canada in 1957 or a little later in1958. So that's probably the earliest an Efkay branded Paiste could be from.