If it is actually meant to work only on weapons (or only specific items) then it should state so on the Coal item itself. Given the density of decisions you need to make, and the impact on any given run each and every decision that you do make can have on a run, there really shouldn't be any ambiguous descriptions.
I do not have the item description in front of me at this very moment but I am fairly certain that is says something along the lines of "refreshes all items that are in the same row". Nothing in the current description gives any indication that it doesn't work on specific items.