It always generates with six item sockets; it is not possible to add another socket using an Artificer's OrbArtificer's OrbStack Size: 20Adds a Rune Socket to a Martial Weapon, wand, staff or ArmourRight click this item then left click a Martial Weapon, wand, staff or Armour to apply it. or a Vaal OrbVaal OrbStack Size: 20Modifies an item unpredictably and Corrupts itRight click this item then left click an item to corrupt it. Corrupted items cannot be modified again..
Item acquisition
Tabula Rasa can drop anywhere.
Although it is possible to use an Orb of ChanceOrb of ChanceStack Size: 10Unpredictably either upgrades a Normal item to Unique rarity or destroys itRight click this item then left click a normal item to apply it. to obtain this item, the item's base type, GarmentGarment, does not normally drop, and can only be obtained by corrupting a Tabula Rasa into a rare item, then vendoring 5 copies to receive a non-corrupted base item.
GarmentGarment
.
Artificer's OrbArtificer's OrbStack Size: 20Adds a Rune Socket to a Martial Weapon, wand, staff or ArmourRight click this item then left click a Martial Weapon, wand, staff or Armour to apply it.
or a 
Vaal OrbVaal OrbStack Size: 20Modifies an item unpredictably and Corrupts itRight click this item then left click an item to corrupt it. Corrupted items cannot be modified again.
.
Orb of ChanceOrb of ChanceStack Size: 10Unpredictably either upgrades a Normal item to Unique rarity or destroys itRight click this item then left click a normal item to apply it.
to obtain this item, the item's base type,