My guess would be that the right one has a 50% chance of being the + terminal. Apply 16V and if it doesn't pop, the probability goes up to >90%, and so forth.
If you have a large lot of these creatures, what is ±1 more or less?
John
Edit: Actually, you don't need the full 16V to pop it. 12V should be more than enough. A reverse-connected tantalum can die with great panache.
I see from the pic that you've wisely got it in a saucepan already, obviously expecting the pop .
Is there no tiny + mark? (might need a magnifier to see it).
When I read your post I started to laugh. It is not a saucepan but a ...magnifier. I use it for soldering...and for the pictures. Struggled for years to keep them close the camera on a steady / convenient position.
John,
Just in case I will test it with the bent lead to +12V.