Okay, the elven caravan arrived and I can finally respond. They got offended in spite of a tedious check of all item decorations, but I got the info I needed.
The issue however is that by laws of priority, when shift-clicked to move all your accessible goods for trade in the menu, it clicks the umbrella bin first, additionally by mis-click the bin can be selected and your previously selected arrangement of goods lost
And when i have 100+ exceptional mussel shell bracelets to sell to some gullible poor mug via my seafood production lines (I'm quite fond of bone-crafters really), it's a real workout to click all the contents.
Looks like a macro is the only good way to speed this up. There's some DFHack keybind for trading that essentially just does a 10 item selection macro. (This is why I had to double check to see what shift-enter did. I think the DFHack one is shift-space or something.) Selecting the items without bins isn't any more tedious than selecting the goods you're going to be buying. (Perhaps much less so because the goods you're selling were filtered by bringing them to the depot.)
Selling the bin also can be a clincher for additional profit in the traders aid (in addition to metals like zinc and aluminum being light enough to not eat valuable time hauling) to make them like you more even if you have diddly squat to offer them (say if a unfortunate accident occurred and a FB battered your food/trade good industry workers into dust)
It's not an economically sensible use of the material. Statues, etc. give more value for the exact same resources. Aluminum is still twice as heavy as the heaviest wood, and about four times as much as the average.
Elves barely comprehend what charcoal is (obviously not enough to get disgusted and pretty much become a sulking civ in terms of behavior), let alone the methods to make metal.
I'm talking about the principle of the thing. Tree-huggers don't deserve dwarven metal.
And im not really sure what you're doing or how you're doing metal wise if you can't make enough to import meltables and a reasonable amount of ores to run workshops to replace what you lose (buying up entire caravan food supplies in bulk to fuel more lavish and exotic kitchen meals for instance as a example)
I make enough value in hunted/grown prepared meals that I wouldn't know what to do with the surplus food bought. It's not the price of the metals that's the problem, it's the supply. Elves certainly won't sell me ores. Humans only bring a few aluminum items. Dwarves will, but you have to fiddle with the supply screen each year to get a reasonable amount. Then, after that, the items need to be marked for melting, hauled all the way to your smelters, melted, then turned into bins. Sure, you'll get some nice exp, but it takes forever, appeases the elves, and it's many more key presses than simply keeping your bins.