Add capability for a single page

This seems like it should be very easy but I’m having the hardest time.
I want to grant the capabilities ‘edit_pages” and ‘edit_published_pages’ to the subscriber role but only for one page.

//If I can use if
(current_user_can('edit_page',594),
//Then it would seem logical that I could use $role->add_cap('edit_page',594)

Unfortunately I’m not having much luck.