Those optics are very fragile, and can easily be damaged!
Alcohol can cause little cracks in the surface.. Proper cleaning can only be done with the softest cloth you can find, with demineralized water and a drop of clear liquid-soap.
But even then, they can easily be scratched!
The only way to prevent this, is to threat them with very much care: Never ever touch the reflective surface !! Keep them dustfree packed until you can mount them.
Only then, you can enjoy the more then 90% efficiency, an efficiency that NEVER can be reached with conventional reflectors!!
Edit: OOPS... I didn't realise you were refering to the dome of the emitter itself!! Silly me !!
Oh well,, the above still stands! Hopefully I will receive my first seoul-emitters within a few days. I never knew they have a silicon-dome !
With this information, I think the way Mac came up with below this, propably is the best way to clean them !
Regards,
Ra.