There has always been rumbling that spice makers secretly add flour to stretch out their spices and the outright incorrect information that silicon dioxide used to keep spices from clumping contains gluten.
There has also been some concern that cross contamination, perhaps from seasoning mixes that sometimes do contain gluten, might be a problem. But many of the big spice companies say outright that their pure spices are gluten free. And we now have testing results to give us the facts about spices. Read the gluten test findings here.