Clay

As I stood there in the clearing, I rolled up my heavily worn sleeves. This was gonna get messy...

I approached the left-most mound. This particular material seemed the least practical of the bunch. I hadn't outright eliminated it from potential materials since it was by far the coolest colour. With only two exceptions, the other ten mounds were only variants on the red pigment. This particular material was wholly blue in nature. That alone piqued my curiosity. In their current states, they'd prove rather useless to me. I had to figure out three main characteristics for smithing, their heat tolerance, their malleability, and their overall scarcity.

Tearing away a handful of the blue material, I headed to the riverside before soaking the material. Reactivating its wet properties. I quickly reshaped the material into the best brick shape I could manage before drying the material with a constant breath of fire. This process, altogether took me a few minutes. I repeated the whole process for the other 11 mounds, 5 of which didn't take to the heating and couldn't harden properly. That left me with 7 bricks. I piled them onto a pile before proceeding with my next test, continuous high temperatures. To my surprise, all but three of the bricks eventually broke down under the prolonged exposure to my fire. Although I had grown immune to my fire, the heat barely being felt on my skin, the effect of the flames was as clear as day. The flames were ravenous and scorching, often extinguishing themselves as they themselves devoured its fuel before it even had the chance to spread.

Before proceeding, I cleaned up the failed materials and through them back into the small river. To my misfortune, the three coloured materials had been by far the most uncommon of all the batches. In a split second judgement, I decided that I'd use all three. Their scarcity would prove too much of a problem otherwise...

Having determined which of the materials would be good clay substitutes, I started to walk towards the tree-line in order to collect some bark to create proper moulds. Using my enhanced strength, tearing flat chunks of bark off was an easy task, except... that once I had torn a few flat pieces, I heard a faint flat tone emanating from the cave.

I don't know how to describe it but... it felt like it was calling me...