Also, you should tell us what the last two metals are.
The last two metals are Chromium and Nicrosil. We'll reveal what they do on the Allomancy poster. Suffice it to say that in the next trilogy, the main protagonist would be a Nicrosil Misting. And, to make a Robert Jordan-type comment, what those two metals do should become obvious to the serious student of Allomancy... (It has to do with the nature of the metal groupings.)
If I read the poster correctly, and have the correlations down, these metals are the external enhancement metals.
The simplest idea is that they do to another person what Aluminum and Duralumin do to the Allomancer burning them. If this is true, then Chromium would destroy another Allomancer's metals (useful skill, that, especially in a group of Mistings fighting a Mistborn) while Nicrosil would cause the target's metals that are currently burning to be burned in a brief, intense flash. This could be used either to enhance a group of Mistings or to seriously mess up an enemy Allomancer.
The other metals do not have exact one-to-one power correlations like that, so it seems more likely to me that they would work differently. It could be like an area effect weakening or enhancing spell. You would want an enhancer in your party, and you wouldn't want to go up against a weakener.
Nicrosil is a rather more complicated alloy than the others. It's an interesting one to pick, rather than something simpler like nichrome (though I guess that's actually a brand name)
Ookla is right, the others don't have 1/1 correlations. But I liked this concept far too much not to use it.
In a future book series, Mistborn will also have become things of legend. The bloodlines will have become diluted to the point that there are no Mistborn, only Mistings—however, the latter are far more common. In this environment, a Nicrosil Misting could be invaluable both as an enhancer to your own team or a weapon to use against unsuspecting other Mistings.
I take it either Spook did not have children or Sazed made him a reduced-strength Mistborn rather than giving him the full potency of the 9 originals and Elend?
Spook is a reduced power Mistborn.
Very interesting about the Nicrosil.
So, if there is no more atium, then that would mean in any future trilogy, there would only be 14 metals, right? Somehow, that doesn't seem right, but maybe that is because it irks me that one quartet to be left incomplete with the absence of atium.
Would it be possible for Sazed to create a replacement metal, by chance, or will the temporal quartet remain inherently empty? It doesn't seem like it's too far of a stretch for Sazed to make more metals: after all, the metal Elend ate was a fragment of Preservation, and now Sazed holds Preservation.
That's a RAFO, I'm afraid. Suffice it to say that what the characters think they understand about the metals, they don't QUITE get right. If you study the interaction between the temporal metals, you might notice an inconsistency in the way they work...
Uh-huh. That was already noticed by theorizers in the forums here. Gold works like Malatium and Electrum works like Atium. Yet they're on opposite corners of the metal square.
Ah. I wondered if that had been noticed.