This only works with Rare (Green) or better weapons, as you have the Affix gained with the sixth upgrade.
You can use the Soulforge to level up Ingots at a 10:1 ratio.
You cannot currently degrade higher tier Ingots to lower tier.
Ingots can be obtained through winning in PvP; Guild Wars & Arena modes with wins.
It is also possible to obtain through Gem Chests; Invasion & Siege shops; and Weapon Bundles.
Rarely can be obtained in Boss Events (Siege and Portal).
After achieving the Affix on the 6th Upgrade, use the weapon in any mode to use its' power and trophy will pop.