Oil on the threads, black carbon, stripes on the insulator ... What will the spark plugs tell you?

Oil on the candle thread, black carbon deposits, stripes on the insulator, white candles, red candles, yellow ring on the insulator ... What will the spark plugs tell you about?
1:28 Point one: when there is oil on the spark plug thread.
2:01 Point two: black velvet soot on candles
4:04 Point three: thin stripes on the electrode insulator
4:53 # 4: White deposits on the candle
5:57 Point five: red or ginger candles
6:36 Clause 6: Dark yellow halo on candle insulator