EDITOR'S NOTE: what follows here is excerpted from a letter to corax from a learned colleague, in response to some technical questions about the chinese tea-terms 清香 and 浓香. published by permission.
First are the terms themselves. Qing Xiang [[清香]] meaning Clear Fragrance, i.e. light, thin fragrance. Nong Xiang [[浓香]] refers to Dense fragrance -- i.e. thick, heavy fragrance.
Then there is the tea. The fragrance of tea is not singular, but often of many textures. What determines the fragrance of the tea is its initial and immediate processes. The end process, which usually is the roasting, enhances the earlier fragrance. Let me explain what this entails ...
Non-oxidation: Leafy, grassy fragrance. If the volatile essential oils compound in the tea gives off a light grassy fragrance, the fragrance is considered Qing Xiang; however, if the grassy fragrance turns heavy with notes of sweetness due to a higher amount of volatile essential oils escaping, then it becomes Nong Xiang. In this case, it has nothing to do with roasting.
Light oxidation: Light floral fragrance, as in Baozhong; this is Qing Xiang. If I were to roast it, the fragrance would change, becoming more settled, more 'cooked' -- we call this 'Shu' Hua (floral) fragrance, but still not Nong Xiang, because the heavy fragrance does not last.
Medium oxidation: TGY, heavy fruity and deep floral fragrance, it lasts in the bottom of the cup. This is Nong Xiang. Roasting it will again settle the fragrance, the 'cooked' fragrance - we call it 'Shu' Guo (fruit) Xiang.
Full oxidation: Black Tea, heavy fragrance, Nong Xiang, roast or no roast.
Qing Xiang & Nong Xiang apply to all fragrances in tea, not just oolong. It is mainly determined by the amount of oxidation, not roasting, though in certain cases, roasting does appear to make it Nong Xiang, but not necessarily so.