The bronze basin (Ex 38:8-38:8)

“He made the basin of bronze and its stand of bronze, from the mirrors of the women who served at the entrance to the tent of meeting.”

The artisan made a bronze washing basin and stand, as prescribed in chapter 30.  However, there is a strange mention of where the bronze comes from.  Apparently it came from the mirrors of the women who served at the entrance to the tent of meeting.  This is the first mention of mirrors.  Who are these ladies and what do they do?  From this text it is not clear whether they have any official role or not.