Nicotine reidue on drivers

In fact what you observed is what would happen if the Beryllium was vapor deposited onto an untreated or poorly treated polypropylene surface.

It wasn’t a causal light wipe, thinking they were pure Beryllium and nothing else, and could take some cleaning solvents like metho, turps which shouldn’t effect Beryllium.
I wiped lightly what looked to be nicotine stains with dust embedded in it, almost salt air corrosion to look at, on the tops of the mid and tweeter domes. With cotton buds moistened with mentholated spirit, after a few light wipes I could see through the dome where I wiped, being a clear polypropylene dome.
Lucky I had a store back then of a few JA0548A and JA0803 which are the Yamaha part no’s for the mid and tweeter.

Cheers George

What you have to think about is, can it be possible to stiffen a polypropylene cone just with vapor deposited Beryllium partials on it.
To be honest I don't think so, as the Beryillium particles would have no structural strength in either plane at all, unless it's spun or forged as in the GF-1's then there's no need for a polypropylene former under it.

Cheers George  

I forgot to add, vapor deposited Beryllium would never adhere to polypropylene without a surface treatment.

 Well once the Beryllium was wiped off all that was left was a clear see though flexible cone under it.

Cheers George  

mizike OP
Is there a safe and effective way to get old nicotine residue
 off speaker drivers? Yamaha NS 1000m
  Thanks, all. I was hoping to hear from someone who had actually tried this.

No leave them be don't listen to anyone saying to clean them, I have and was shocked, the mid and tweeter on theNS 1000, 1000x and 2000, are clear polypropylene cones, that just have a very thin vapor deposited coating of Beryllium on the polypropylene, any cleaning or rubbing will take it off and expose the clear polypropylene cone underneath.
Only one or two Yamaha's had pure spun Beryllium cones, and were as fagile as egg shells, the mighty GF-1
https://www.hifido.co.jp/sold/14-84924-31512-50.html?LNG=E
 and I think the NS10000 also.
  https://www.hifido.co.jp/sold/16-06185-99993-50.html?LNG=E

Cheers George