The 18" is either a Crash or a Crash Ride. The relatively larger bell tells me that. You would need the weight to have any chance of pinning down the difference.

The 20" is some sort of Ride. But you knew that already. The model choices for the 1960s to early 70s models for drum set are Medium or Ping, but they also called some BOP and some Bounce. And there may be other models like Band, Dance, and Orchestra. I've collected up examples of the model ink from that era but I don't expect I've got them all yet. But once the ink is gone it's the weight which can give you a hint.

Expected prices are here for 20" http://black.net.nz/avedis/avedis-prices.html#20

and here for 18" http://black.net.nz/avedis/avedis-prices.html#18

Thank you.

18” Zildjian crash cymbal (1550 gr) and 20” Zildjian ride cymbal (2130 gr)

You've taken really nice care of those. They look great!

Thanks, Mike. I have gigged with them off and on for over 40 years. I clean them regularly (gasp!) and store them in terry cloth bags when not set up to play.

I'd say 2130g is a Medium Ride for that era.

I'll have to check my database and see what the distribution of weights is for 18" cymbals in this era. I've got a 1250g 18" from that era which is obviously a Crash. But 1550g I'm not sure about. Could be a Medium Crash or Crash Ride (which some people claim were only different in the ink applied) but it's unlikely to be a Ride.

So here are some weights for 18" cymbals where there was still model ink:

FAST CRASH 1285g

THIN CRASH 967g*, 1337g, 1362g, 1364g, 1376g

MEDIUM CRASH 1361g, 1475g, 1535g, 1563g, 1581g

MEDIUM THIN 1433g, 1440g, 1448g

MEDIUM THIN CRASH 1448g, 1454g

CRASH 1450g (suspect this was a MEDIUM CRASH or MEDIUM THIN CRASH with incomplete ink)

DANCE THIN 1376g, 1390g

MEDIUM 1500g, 1540g

then there are MEDIUM RIDEs (1595g to 1723g) and they don't have the larger bell. They have the same size bell (5") as the 20" ride cymbals.

So you can see why it's both hard to be sure of the exact model, yet there is also a pattern to the weights. Yours fits the MEDIUM CRASH weight, but there are also cymbals which just said MEDIUM. Note I haven't seen an 18" cymbal with CRASH RIDE ink which has a 60s stamp or a 70s stamp. Maybe they were calling them just MEDIUM back then. I'll have to cross check with ads and catalogs to see if we can pin down when CRASH RIDE ink first appeared. Maybe it was around in the 60s and I just haven't spotted one. Cymbals with ink are rare enough that I might just not have seen a CRASH RIDE yet in 18". So rare that a number of people still haven't caught on to the fact that Avedis Zildjian started putting model ink on in the 1930s.

Hope this helps.

* here is the 967g one: http://www.vintagedrumforum.com/showthread.php?t=59359