tarry deposit in wok
If your wok is coating-free, use oven cleaner. Spray it on, place it in a plastic bag, &amp; give it a few hours/overnight (best) to work. It should all wash out easily the next day. Wash well, dry, &amp; re-oil w/olive oil, etc.

PS: this also works wonderfully with those enamel-on-steel pots &amp; similar stovetops.