Tier
All crafted items are divided into tiers. Higher-tiered items have either better stats or more stats. The tier of a crafted item is determined by its component parts: tier-1 items are crafted from gathered resources; crafting items of subsequent tiers requires items of the previous tier. An item's tier can usually be recognised by the number of bonus stats it has.
Bonuses
Upon increasing an item's tier, that item gets either better stats or more stats. This is implemented differently in each crafting profession.
Alchemy
Higher-tiered consumables crafted with Alchemy have a longer duration and better stats.
For items with more primary stats, the player must have a higher Mastery Level.
Construction
All tier-1 Artifacts crafted with the Construction profession have 1 primary stat. Artifacts of subsequent tiers have the combined primary stats of the items used to craft it.
Mysticism
As the tier of runes crafted using Mysticism increases, the item's stats are randomly chosen between a higher upper and lower boundaries.
To increase a rune's primary stats, players must craft the rune using higher-quality items.
Weaponsmithing
Higher tiers of chips crafted using Weaponsmithing have increased upper and lower boundaries from which the item's stats are randomly chosen between.
To increase the number of upgrade slots a weapon has, the weapon must be of higher quality.