How to open 10 gem slots in equipment

Hello. I have a character level 100, with more than 5 years old, and with more than 8,000 achievements.
I have all level 140 gear, and some unique ones.
The only mission I need to finish is to kill Gorga in the parallel world, one more time.
My character is the only one I have at level 100.
I ask: Does anyone know why the game doesn't let me open more than eight sockets (in all the pieces)?
Is it necessary to be premium to open them, or is there a special achievement?
From already thank you very much.

 

hi.. in legendary things it is impossible to drill 10 slots, maximum only 8.. and 10 slots can be drilled in unique things..

I would advise you to start another 3 characters, each character at the entrance to the game, will give 50 andermants daily, and this is not many or few 200 andermants a day without a premium.. it is also an opportunity to go through some events and receive a free premium 4 times..

 

By the way, the number of gem slot is error. My DK has the number 7 from the statement of map entrance. Unique, white items and gem/jewel trinket are all 7 slots, but improved/magic/extraordinary/legendary items (no matter loot or crafting) are 6 slots.

Thanks!

 

Thank you very much for your reply