This fireplace is in the house we are currently renovating to sell. My wife whitewashed the brick(it was pretty ugly) and we made a mantle from a few pieces of reclamed barn lumber. I think it turned out pretty nice.
No creosote just really ugly brick. We thought it was fake bc it almost looked like the fake ones you can buy. But it was real.
I don't know what it served exactly. And yes they are mortises. It came from a barn the collapsed close to where I live.
Not to derail, but got a bunch of these from a collapsed barn, years ago... I'm down to maybe 2... They've been used as pegs in coat racks. Old timey! Came from a barn on my friend's property where the "Great Lakes to Florida" trail passed thru... Part of that old wagon trail is still visible in the lower 40 on their farm. Neat stuff!