Grinding
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Grinding is the step where you either preserve what you bought or destroy a third of it, and the difference is almost entirely about temperature.
Heat is the enemy and you are making it
A mill does not cut, it fractures, and fracturing is inefficient: most of the energy becomes heat. In ambient grinding the mill can reach around 95 °C. The documented consequences are a loss of roughly 30 percent of volatile content and a darker powder.
Every minute the mill runs continuously, it gets hotter and the loss gets worse. The last jar off a long run is not the same product as the first.
What industry does about it
Cryogenic grinding. Liquid nitrogen at −195.6 °C pre-chills the material and holds the mill cold. Two things follow. The oils solidify, so the spice becomes brittle and fractures cleanly instead of smearing, which lets the mill reach 80 mesh or finer. And the nitrogen boiling off displaces the air, so the grind happens in an inert, dry atmosphere.
It consumes around three quarters of a pound of liquid nitrogen per pound of spice, which is why it is an industrial process and not a small one.
What you can do about it
You cannot buy the cold. You can buy the principle, which is keep the material and the mill from getting hot.
Grind in short bursts rather than continuously. Let the mill cool between batches rather than running it all afternoon. Grind small quantities close to when you will fill, so the product spends its life whole rather than powdered. Chill the material and the mill parts beforehand if you have the freezer space; it is a crude version of the same idea and it measurably helps.
Done this way a small operation genuinely produces a fresher ground spice than a commodity mill, which is not something you can say about most steps.
Between materials
Clean properly between spices and run mild to strong. Residue in a mill transfers to the next material, and the mill is the single worst point for aroma carryover in the whole operation.