a small suggestion that I think would be fair. I think the last class of gems (Perfect) should have a slightly larger bonus than the rest, because currently I do not think that that grant bonus compared to the previous two to them (Flawless and Pure) is attractive to devote the time it can take to create them, I have no doubt that should be a few more days.
and I rely on a simple calculation: if it takes 3 days to create a Flawless Gem to create a Perfect would need 12 days more for a total of 15 days and just to get me in the case of damage only 1% more setting an example.
Now I bring my suggestion of bonus they should have and I think it should be 10% minimum and 20% maximum which now give the midpoint seeking a balance between those two would be a 15%
Welcome be other contributions and suggestions they wish to and I would like to express your opinion. 

