What am I looking at here?

[Tomed]

Cleaned off the bottom board 8 hours ago. New beekeeper. Nuc only installed 1 week ago

[JeffH]

The large bits are chalk brood mummies. I’m not sure what the blackish gritty stuff is. The lighter colored stuff is most likely brood cappings created while young bees emerge.

[Eva]

The black bits might be mildewed wax. Your hive might need some help with ventilation.

[chau06]

I was thinking the black bits were some sort of frass.