I just finished some post-Ambitions testing. Here are the results, all using the 2 & 7 method:
Small Platinum--Large Platinum & Large Compendium
Small Palladium--Large Palladium & Large Iridium
Small Silver--Large Silver & Large Plutonium
Small Gold--Large Gold & Large Iron
Small Iron--Large Iron & Large Iridium
Small Supernovium--Large Supernovium & Large Compendium
I didn't have enough of the other metals to test them, and I'm still not sure if I have to stack two large mercury ingots or if I can get away with just one and seven vials.
ETA: I still need to stack two mercury ingots, but I somehow got small mercury ingots in my Sim's inventory.
Small Mercury Ingots (2) & Mercury Vials (7)--Large Mercury & Large Platinum
Large Mercury Ingots (2) & Mercury Vials (7)--Large Mercury, Large Platinum, & Large Iron