I've tried letting silver coins soak in WD40 for a few days. It must be pretty mild because it doesn't remove the toning and doesn't even do a very good job cleaning other "stuff" off of the coin, but I haven't noticed any long term damage from using it for improving lightly soiled coins.
Acetone is Dangerous Just in case the someone reading this doesn't know.....here is an excerpt from an MSDS for Acetone: "Danger! Extremely flammable liquid and vapor. Vapors may cause flash fire or explosion. Harmful if inhaled. Vapor concentrations may cause drowsiness. Causes skin and eye irritation. Harmful if swallowed. May cause target organ or system damage to the following: Eye, skin, respiratory system, central nervous system." Many people tend to wave off warning labels, but acetone is very dangerous, especially in a poorly ventilated area.
Whats the differance?You send a coin to NGC they body bag it send it back to you with a note to send it to NCS and tell you "Thanks for submitting your coin for grading but we are unable to grade your coin "-THANKS FOR THE MONEY
Big difference. Because if you send it to NCS first with instructions to send it on to NGC, if they can conserve it, you will get the coin back in a slab instead of a body bag.
They are sister companies. Each is an independent entity...they just fly the same flag (Collectors Society).