The phrase "inert substance" refers to a material or substance that does not react or change when exposed to other substances or outside influences. It remains stable and unaffected in most situations. Full definition
When I use malachite and lapis pigments mixed in glue - size and scraped into a coarse linen canvas, I can't help but see them as inert substances but also simultaneously as the dusk of Iceland and the atmosphere in the cloister of San Marco in Florence. (artinamericamagazine.com)
The NOP regulations currently allow for synthetic inerts to be used in conjunction with approved active pesticide ingredients, provided that the synthetic inert substances are: (rodaleinstitute.org)
Silica is also a physically and chemically inert substance, and is a major component found in ordinary sand. (pets.webmd.com)