Pro tip: I was cleaning the smoke shelf wrong for 9 years until a homeowner in Dayton watched me do it
I always scraped the smoke shelf with a flat wire brush and called it done, because that's how the guy who trained me in 2015 did it. Last Tuesday a retired mason in Dayton stood at the fireplace and said "son, you're just pushing the creosote flakes back onto the damper." He handed me a small mirror and a bent piece of coat hanger, and sure enough there was a ridge of glaze packed behind the shelf lip I'd been missing at every job. Now I tape a mirror to my vacuum hose so I can actually see back there before I scrape. Anybody else got a homemade tool for the spots your brushes won't reach?
That mirror trick is so smart, I'm stealing it. My version of a homemade tool is a paint stir stick with a strip of old tee shirt wrapped and rubber banded around the end. Sounds dumb but it works great for wiping glaze off the shelf lip because it bends where your hand won't fit. Learned that one after a sweep in an old farmhouse where the shelf had a lip so deep my brush never touched the back wall. I ran my phone camera back there on video just to check and the whole back edge was still black and shiny. Now I do the stir stick wipe first, then scrape, then check with the camera before I call it clean. That step adds maybe three minutes a job but it's saved me from a callback more than once.