According to the information you provided, a layer of white substance appears on the fermentation of pomegranate wine, which may be the fermentation product of yeast or other microorganisms. The black substance may be oxidized pigment or precipitate. These white and black substances do not necessarily mean that the pomegranate wine has gone bad or is bad.

However, since the nature and origin of these substances cannot be determined, the best course of action is to conduct further observation and tasting. If there is no noticeable change in the taste and smell of the pomegranate wine, fermentation can continue, but make sure the temperature and environmental conditions are suitable for fermentation. If there is an unusual smell or taste, it is recommended to stop drinking and try making it again.

In addition, the fermentation time of pomegranate wine is usually 7-10 days, but the specific time depends on factors such as temperature, yeast type, and pomegranate variety. It is recommended that you pay close attention to the appearance and smell of the wine during fermentation to ensure that it is fermenting properly.