Usually, these three metals are completely priceless in the market, valued far higher than Magic Crystals.
However, Fang Ka didn't plan to use these for trading, but rather to reserve them, and later when his power increases, to forge equipment and weapons, and then perform enchantment.
After all, unlike Magic Crystals, which don't really enhance strength and are only widely used and relatively rare.
But Purple Tungsten, if it can be enchanted excellently, can significantly boost strength.
Fang Ka is a Necromancer, and will certainly be an enemy to all in the future. Trading such items would be aiding the enemy, which Fang Ka definitely doesn't intend to do.
Keeping them for future use is not the point; even if unused, holding onto them is better than letting them fall into others' hands.
