I would suggest leather over armor for tutamen, it's stackable, it's renewable, and you get more bang for your buck. A leather tunic takes eight leather to craft and provides six tutamen, each of those eight leather provide one, the highest number of tutamen icons you'll get from any given chest plate is 9 for the likes of diamond, nano, quantum, etc. The exception being the amethyst chest piece, from Biomes O' Plenty if I'm not mistaken, which provides 13. So you could spend 8 diamonds for 9 tutamen, or 9 leather for the same amount without having to dig around pools of lava deep below ground.