Burning (allomantically) swords.

[Onironte he/him]

 

Shardblade and Shardplates are made up of cognitive shadows (spren). They are also Cultivation and Honor Fragments (because they are metallic).

This presents two unknowns:
How can a divine metal appear and disappear transforming into a cognitive shadow.
What would happen if a Radiant Allomantically burned his Shardblade?

[Quantus he/him]

Spren are pure Investiture.  Generally speaking Investiture can either Invest into a pre-existing object/person, or it can manifest directly as a form of matter itself.  When it does that it takes tons of Investiture (along the lines of manifesting a cheeseburger using electricity and and E=MC^2).  For mostly thematic reasons solid Investiture tends toward metals.  Liquids are the most "powerful" because they are dense but not settled into a specific form and function.  

Spren can manifest their Investiture as a full physical object only when they have enough Connection to something in the Physical realm to act as an anchor, which the Radiant Bond provides.  

Cognitive Shadows are also Pure Investiture and are functionally very similar to Spren, but they are distinct in a few ways.  The biggest Ive seen is that Cogntive Shadows were once mortal (with their own physical form) and unless they were restored nice and quick (like Szeth) they need some external Investiture to support them (weekly Breaths, Oathpacts and other massive infusion of Investiture by a Shard, etc).  I suspect that Spren dont require the same sustaining external Investiture because they arent being Pulled to the Beyond; but Beyond questions get no answer as a matter of policy.  

 

 

Burning a Rosharan Godmetal may or may not work out of the box (without a Connection to those Shards), but it would be viable, not inert.  The most recent answer is "it would do something".  We do know of that one Allomancer that has a tie to Rosharan magics now, so he might be able to do it.  I assume it would be harmful to the spren, though Plate might be able to heal with Stormlight.  I'll be curious to see if different Plate that comes from different species would have different effects (windspren vs glory or logic or creationspren, etc).

 

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word_thief

What would happen if a Mistborn ingested the metal of a Shardblade/Plate?

Brandon Sanderson

A Shardblade is Invested. A Mistborn isn't likely to have a tie to that type of Investiture. So probably nothing would happen…

General Twitter 2013 (Oct. 24, 2013)

 

 

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Questioner

If a Mistborn were to burn a piece of a Shardblade, what would happen?

Brandon Sanderson

This would be hard to make happen, but it would be possible. A Shardblade is going to act as, basically, an alloy of the god metal of Honor and so  what would it do? RAFO, but it is possible and it would do something. It would not be inert. It would be Allomantically viable.

Footnote: This question was also addressed here.
Starsight Release Party (Nov. 26, 2019)

 

 

 

 

[Dunkum he/him]

spren are not generally cognitive shadows. the Stormfather is, but most are not.  as to your questions:
1. just like matter and energy can be transformed into one another IRL, investiture can be converted to matter and/or energy.  godmetals, such as Atium, Lerasium, Trellium, Harmonium/Sazdium and yes Shardblades and, presumably, shardplate are basically just investiture that has been converted into solid matter.

2. probably something, but we don't know precisely what. there would likely be some kin of allomantic effect, and also it would probably not be pleasant for the spren to have part of itself burned that way. but without having seen this happen we don't know what the result would be.

[Onironte he/him]

Thanks.