It's for leveling up your sword via a swordsmith in major townships.
A few notes on ingredients.
• Supplies can be found absolutely anywhere.
• Iron is found mainly in Mongol territory, but can be found in minor townships and in some cases inside the homes/forges of Swordsmiths.
•Gold is ONLY found in Mongol territory or given as an reward for liberating Mongol Territory.
• Steel is majoritively found within Mongol territory, but can be found in townships in some rare instances.