I know that silver tarnishes but isn't that just on the surface unlike rust?
But would silver tarnish "where it matters" meaning where the lug and binding post are clamping and making contact with one another? Or would the surfaces be essentially sealed keeping the tarnish only on the outside where it would be unsightly but not impact the connection?
I guess if one were truly dedicated you could solder the silver cable to the silver binding posts on both the amp and speakers...
Yes, and no. While it's true silver tarnishes and oxides form worse when it's directly exposed to air, it also tarnishes when silver banana plugs are plugged into speaker banana jacks of less noble metals of a different material through galvanic corrosion and chemical transfer with even the tiniest hint of air surrounding the metal to metal connection. This is why silver always has to be completely plated, sealed, or insulated in another material that covers it from the atmosphere
completely. For instance, my KLEI Classic Harmony silver banana plugs became heavily tarnished after being plugged into my Vandersteens for awhile. The only way to truly get real silver not to tarnish or corrode is when it's a base metal that has been plated over, or when it's behind film insulation -like in cables and wires.
This is why bare silver can sometimes act as a cancer to mating metals where it can actually remove the plating material of the mating metal by reacting with ambient sulfur compounds in the atmosphere, such as hydrogen sulfide and sulfur dioxide, causing plated jacks (mine were copper underneath) to also start tarnishing in the future whereas they never tarnished before because their thin, plating metal was protecting them from tarnishing. This can end in a constant maintenance loop, where not only does the silver on the connector itself start to tarnish even when it's plugged in and doesn't seem like it's exposed to "air", but it can also create new tarnish or oxides to form or be deposited or transferred onto the plating metal of the jacks which over time, has eaten through some of my jacks to expose the copper underneath them which then starts tarnishing as well. It can be a vicious cycle.
This is how I learned my lesson to try and avoid anything that has naked silver on the outside of it as much as possible. Silver can be seductive. Bare silver is more revealing than anything else (at first) but slowly diminishes over time without you noticing it because the process is so gradual. To me, it isn't worth it in the long-run. While silver oxides/ sulfides are not the worst dielectric, they also don't sound nearly as clean and detailed as fresh silver. After listening to tarnished silver connectors and then cleaning them with deoxit and listening afterwards; the difference was that the music was slightly more muffled and recessed before the cleaning of the silver connectors and their mating jacks which had also become dirty/ tarnished because of it. This finding was significant and impactful, and why (to me) the ideal metal for banana plugs or binding posts/ jacks would be silver as the base metal (which is the most conductive metal), plated in gold (which is the most conductive plating material that doesn't tarnish). Pure copper plated in gold comes in at a close second and remains the only readily available choice between the two for some reason.
EDIT: To Lou G's point, yes, if you can find bare/ exposed silver that claims to have that clear, protective passivating layer over it, you may be able to get away with it. I just haven't found many bare silver audio products that claim to have that protective layer, at all, and am unsure of its effect on silver's otherwise excellent conductivity. I don't think the data or information exists which states how much (if at all) a clear, protective layer on silver impedes its performance. If they don't mention this clear, protective layer in the silver product's advertising, then they don't have it and any exposed silver will eventually form a grayish, less-conductive layer on the outside of it over time.
