Daddi Triptych

The Courtauld Institute has a very nice feature about a triptych painted in 1338 by Bernardo Daddi. 

You can view it closed, as it might have been during most of the year.   
And then you can see it open, as it would have been on a major feast day.

There is a good deal of material here, although each page is short and sweet.  You can read see, and read about, the following -

background to the triptych and its painter.

its context.

its production (You can also watch seven short videos on that process!) 

You can also examine each part of the triptych up close --

exterior (closed); and interior -

scenes of the Nativity story, at inner left (open)

Virgin and Child enthroned, at inner centre (open); and

Christ's crucifixion, at inner right (open).