作为以下意思的时候可数：
[C]dirty mark or patch of colour caused by staining (stainv 1) 污点; 污斑; 污迹: There's an ink stain on your shirt. 你的衬衫上有一个墨水斑. * I can't get these coffee stains out of the carpet. 我弄不掉地毯上的咖啡污迹. [C] thing that causes disgrace (to a person's reputation, etc); moral blemish 玷污（某人名声等的）事物; 品德上的污点: He left the court without a stain on his character. 他经法庭一役, 人格丝毫无损.
作为以下意思的时候一般不可数，但有时也可数（比如最后一例句）
[U, C] liquid, etc used for staining wood, fabric, etc; dye 染色剂; 着色剂;
染料; 颜料: How much stain should I buy for the table? 给这张桌子上色, 我得买多少颜料? * a range of wood stains 木材着色剂系列.
参考资料：牛津高阶