By melting Bares Longbow using Heating Process I received:
3x Trace of Battle
1x Pure Platinum Crystal

Credit to the comment here: Materials for Skills. The necessary quest to process this item starts with the Quest "Excellent Magnate". You must be Skilled 10 in Gathering and Professional 5 in processing to accept the quest from the "Villager" (he's right behind the blacksmith in Keplan). Just use the search utility, and click the "Repair" button when in Keplan. The "Villager" actually instructs you to speak with Vatudun (who's in the cave in Keplan). Vatudun is the NPC that completes the 2nd and 3rd quests in this chain "A Man Better than Coal (?)" and "Materials for Skills", respectively. The "Materials for Skills" quest is the one that actually unlocks the knowledge to process this item yourself!

"krochlikmiov 4-04-2016 18:47
Requires Skilled 10 Gathering and Prof. 5 Processing despite what the tooltip on many items say.

This quest is actually given by an NPC simply named Villager. The villager is located in Keplan, inside the smithy, behind the armorer and the NPC that exchanges seals. This quest leads you to the NPC Vatudun."