Recently I was reading Warbreaker and an interesting though occurred to me. Could Denth be a mistborn (or at least a misting)? He is said to have, and is proven to have almost superhuman speed, much faster then the Returned. He could have burned pewter to make this happen. He also may have been burning brass to get Vivenna to like him, Tonk Fa, and Jewels more than she would normally and keep her placid and unaware of what they were doing to her. If he was a full mistborn he would of likely burned zinc as well when creating 'distractions' in Hallandren, making the Idrians angrier and ready to start war with Hallandren.
Denth does say that he came from far away and Vivenna deduced that he seemed not to fit in very well. I think that it may have been possible that when the 5 scholars were forming and there wasn't 5 yet they were traveling via the cognitive realm to Scadrial and picked up Denth there. They then made their way back to Nathalis, gather insane amounts of breath up past the 5th heightening and make Nightblood. Unbeknownst to the rest of the 5, Denth is a mistborn but maybe doesn't know it yet. He may have snapped after Arsteel was killed by Vasher, and then because of his life on Scadrial knows what has happened and starts experimenting and becoming better over hundreds of years.
I think this may work. Let me know what you think.
