Gem tiers provide the multiplier for their bonuses. For example, a regular warrior gem provides a 10% boost to a weapon, whereas a perfect warrior gem provides a 30% boost to the weapon. The regular tier of gem is the most basic and can be found by killing usual treasure orcs. The second tier is carved gems. Carved gems can be found by killing treasure orcs, too, however it is a lot rarer. They can also be found by combining three basic gems. Polished gems are the third tier of gems, and they can be found by killing a treasure olog or combining three carved gems. The fourth tier of gems is refined gems. They can only be made by combining three polished gems, however the result is very much worth it. You might only get these late act II or early act IV. The fifth and final tier of gems is perfect gems. They are only obtainable through combining three refined gems. These gems are incredibly late game items, and you will generally only get them in late shadow wars.