How do Threnodite shades "ruin" silver?

[Ward]

In Shadows for Silence in the Forests of Hell, silver that makes contact with a shade is ruined. It turns black and crumbles. My question: is the ruination a natural process (turning into silver sulphate, or silver bromide, for example), or is the silver transmuted into another element, alchemy-style?

[Spoolofwhool]

Interesting question. My guess is that the shades wither silver similar to how they wither people, which can apparently be described as a "cancerous forging". So in essence, it's physically/spiritually/cognitively changing the silver to a different form and destroying it. 

WoB on the matter:

Quote

KURKISTAN

If you're on Threnody and you get withered by a shade, are you better off burning Allomantic aluminum, or tapping Feruchemical gold?

BRANDON SANDERSON

(lots of laughing) [Some clarification on the question]They would both work pretty well. I would say if you burned aluminum, that would kind of have the effect that you are wanting it to have, which is the effect- negating and sucking out, so that’s probably safer. But the gold would work, too.

KURKISTAN

So would it be fair to describe withering as a kind of cancerous Forging-

BRANDON SANDERSON

Sure.

KURKISTAN

That just kind of slowly takes over your soul?

BRANDON SANDERSON

Sure. That's legit

[Source]

Edited October 24, 2016 by Spoolofwhool

[Landis963 he/him]

We don't know.  There's no indication in-story one way or the other (I assumed it was the silver was rapidly aging (i.e. tarnishing), but that's just how I pictured it).

Edited October 25, 2016 by Landis963

[Ward]

That's what got me. As far as I understand, silver doesn't really "age" because it's so non-reactive. Same as Gold. Silver Jewelry will only tarnish due to the other metals in the alloy being reactive.

And since Brandon started out in Chemistry, I suspect there's something sneaky afoot other than just, "*shrug* it's magic."

Edited October 24, 2016 by Whim

[Brgst13]

First off, I have no evidence to support this theory.  I suspect, however, that this withering is Cognitively-based.  The shades are Cognitive shadows, so they exist at least partially in the Cognitive Realm.  When the shade interacts with the silver, it does so in all three realms.  The "withering" is a result of the shade destroying the cognitive aspect of the silver.  As a result, the physical aspect withers and blackens.

[VirtuousTraveller he/him]

14 hours ago, Brgst13 said:

First off, I have no evidence to support this theory.  I suspect, however, that this withering is Cognitively-based.  The shades are Cognitive shadows, so they exist at least partially in the Cognitive Realm.  When the shade interacts with the silver, it does so in all three realms.  The "withering" is a result of the shade destroying the cognitive aspect of the silver.  As a result, the physical aspect withers and blackens.

When a shardblade cuts through living flesh, it severs the connection it has to the spiritual realm, which causes it to "wither."  I wonder if there's a connection to this.