In Gemcraft 1 and Gemcraft 0 you could combine high level gem with low level gem (difference must be at least 2 grades). It increased the damage, fire rate, range and specials.
I tried to do this in Gemcraft Labyrinth but the damage, fire rate and range got lower. Also when i combined low pure gem into high dual gem, the special from low gem stayed the same and the other has lowered.
So is increasing the gem grade by upgrading, or combining same grades the only way to strengthen a gem (not counting amplifiers of course)?