Act III Materials belong to the Nether and the Alex’s Caves biomes: netherite and other late vanilla materials, Dungeons and Combat ebony and crimson ingots, Alex’s Caves minerals, and the Astral Calamity ingots that lead to the Brimspec Ingot.
Two different Crimson Ingots exist. Dungeons and Combat’s makes crimson tools, weapons and shields; Soulslike Weaponry’s goes into the Duskfire, Nightmare and Bloodcrest Ingots and several blood weapons. Both go into the Bloodcrest Ingot.
Ebony Ingot makes Dungeons and Combat’s ebony tools, long sword and shield, the Eternal Night Scythe and the Twin Shadows.
Alex’s Caves materials are mostly used for that mod’s own gear:
Azure and Scarlet Neodymium make magnets and the magnetic tools.
Pure Darkness makes Shadow Silk, the Dark Gem Of The Living Void and darkness weapons.
Bottles of Radon make the radon lamps and the Polymer Plate.
Tough Hide and Heavy Bone make the Primordial armor.
Gilded Ingot (gold and Lava Power Cells) and Corrupted Ingot (Cursium, Black Steel, Phantom Membranes and Echo Shards) feed the Brimspec Ingot; the Corrupted Ingot also forges the spell Echoes.
Bloodcrest Ingot (both Crimson Ingots and a Blood Orb) upgrades the crimson blood weapons.
Brimspec Ingot (a Nether Star, a Void Core, and a Molten, a Corrupted and a Gilded Ingot; makes 4) is one of the pack’s main upgrade materials: it goes into over 20 Mechanical Fusion Anvil armor and weapon recipes and into the Universium Ingot.