Originally Posted by
ffourteen
Sorry, Oolong is the Anglicized spelling, Wulong is the Mandarin pinyin spelling. Can you elaborate on what you mean when you say "a film"? I don't know much about Indian teas, but I think most are blacks (?); black tea is fermented, and like Oolongs, should have a wash before you steep them. However, black teas do stain (then again, so do greens); in a porcelain pot this would result in a reddish mark, eventually dark brown or black I think, where in an yixing pot you would usually match the color of the clay to the tea (roughly; i.e. not using a yellow or green clay for black tea) and so it wouldn't really leave a mark. Also, if you have 'cracked glaze', on your cups for example, it will darken the cracks (generally considered to be a good thing).
That being said, one of the mains reasons I drink tea instead of coffee is the clean mouthfeel and the freshness afterward (as opposed to coffee breath). Green teas are considered to be "fresher" 爽 than fermented teas, so maybe it's the tea type, and not the origin?