Stove owners blame the stove, the flue, the weather and the sweep. Three times out of four it is the wood, and the three problems below are the same problem wearing different clothes.
Wet wood, or the air closed down too far
Black glass
Below roughly 260°C the smoke does not ignite. Those unburnt particles have to go somewhere, and the coolest surface in the stove is the glass.
The fix Burn drier wood and give it more air for the first twenty minutes. The airwash only works once the fire is properly hot.
Wood too wet, or logs too big too soon
It will not get going
A cold stove needs a small, fierce fire to establish a draught. A big damp log on cold kindling smothers it before the flue warms up.
The fix Kindling, then thin splits, then full logs. Kiln dried lights noticeably faster from cold than seasoned.
The same unburnt smoke, cooled in the flue
Creosote and chimney fires
Creosote is what black glass looks like when it happens up the chimney instead. It builds fastest on damp wood burnt slowly, and it is what actually catches fire.
The fix Dry wood, a hot burn, and a sweep at least once a year. This is the safety argument for dry wood, not just the efficiency one.