Do you know which metal you are pushing/pulling?

[Leviathan]

So, I can't actually spot this one in the rulebook anywhere.
When you burn Iron or Steel and see all your handy little blue lines, are you able to work out what the metal you're detecting actually is? Can you tell the difference between iron/gold/zinc etc?

I'm working on a.. combination lock/safe of sorts that requires pulling the right bits to open it

[SirJerric]

I don't believe you'll find anything in the rule book about it, since the only distinguishable metals in the stories are aluminum and a few of its alloys. These have no lines at all, being "Allomantically inert". Other than this, no primary viewpoint character ever makes a distinction, and the Inquisitor viewpoints aren't detailed or common enough to have hinted if their superior ability in this field allowed such a distinction.

Things to try that have canonical support:
Lines to smaller metals inside larger, hollow metals (sub-lines are less notable at first glance).
Vary object sizes, or have shaped symbols under an obvious surface.

Overcomplicated example:
Thin rods inside hollow cylinders inside the obvious surface object (Push the internal rod while Pulling on the cylinder of the set that is third from the left, and Pull the internal rod of the second set from the right, and Push the cylinder of the leftmost set, while not disturbing any of the others. Do that in order, holding all steps in position, in order to set the first dial of the external twist-knob combination lock. New patterns are required for each external input, plus a final pattern to allow the unlatching mechanism to release. Most of the moving parts are stone, wood, or aluminum to hide the mechanism design from the intruder.)

[Leviathan]

Hrm. Could be good fodder for a stunt

I was thinking of a door lock where you need to pull the right metals, push other ones (can be done by hand), and then release the door at the right time. Was going to involve all the metal symbols in a pattern on the door, and you had to push & pull the ones that had a matching metal behind the symbol (ie, pull the Iron bar behind the Iron symbol, but if you pull the gold bar behind the Atium symbol, TRAP!).

Instead I'll need to go by the symbols themselves, and give a code for figuring out which symbols to use...

[Crafty_Alex]

So, I can't actually spot this one in the rulebook anywhere.
When you burn Iron or Steel and see all your handy little blue lines, are you able to work out what the metal you're detecting actually is? Can you tell the difference between iron/gold/zinc etc?

Definitive answer: No. The only way you can tell what metal is being used via Allomancy at this point is using Copper to sense which metal is being burned.

I do, however, like your idea of making this a Stunt - it doesn't strike me as a game-breaking ability and will only come in really handy in a few circumstances such as those you named. I say go for it!

I'm working on a.. combination lock/safe of sorts that requires pulling the right bits to open it

That...is awesome.