Roshar is the easiest aluminum source

[Stonewardguy]

So, I've seen this mistake a few times and it's starting to bug me. In Words of Radiance on page 562, Shallan is selling her necklace to a debt collector to clear something up for one of her brothers. He says that it is "Simple, but of aluminum, which can only be made by Soulcasting". There is a simple way for radients to get aluminum, so long as they're of the right group as well as anyone who has an actual soulcaster. While it isn't currently common that I can tell, it isn't exceedingly rare and not incredibly hard to make. At the point the cosmere is at, Roshar is likely the easiest place to get aluminum. With this, as it is soulcast, I don't think the stuff he brought to the wall guard in Oathbringer was aluminum, more likely Lerasium or Tanavastium or some other godmetal (I say lerasium because Preservations power seems a good plan when trying to save someone, and Harmonium can be split to get lerasium). I know the aluminum thing was a small detail, and we need to spread this knowledge around the community.

[Kingsdaughter613]

It was aluminum; aluminum is the only Investiture blocking substance we know of.

Apparently it’s not that easy to doulcast aluminum, as it ends up being a major Scadrian export. If it was that simple you’d expect it to be a Rosharan one, but it isn’t.

Considering Lin Davar’s Ghostblood connections, there’s also the possibility that the necklace did not originate on Roshar.

[AquaRegia]

this is a duplicate topic - can it get deleted?