This is possibly the most asked and hardest to answer question we receive.
Diamond disks are subject to a number of variables that will impact the lifespan of the disk. The main variable is how much glass you are grinding with it. If you're just doing surfaces that are smaller and have very little glass to remove to flatten them (i.e. general paperweight use), then the disks will last much longer than when grinding larger surfaces like cast work.
Typically we've seen that a shop that grinds paperweight bottoms using the disks on average about 4 hours a day for 5 days a week will see about 10 months from a set of disks. Higher production shops will see less lifespan, lower production more.
The size of the disk will also affect the lifespan. If you are grinding on a 12 inch disk with a 3 inch bottom, then you are using a significant amount of the area of the disk for a significant time frame. If you work the same piece on a 24 inch disk, then you are using only a fraction of the area of the disk at any one time and therefore not degrading the diamonds nearly as quickly.
These are all variables to take into account when deciding which size and grit disks to get for your particular grinding needs. As always, we are always here to help with any questions in that regard.