Minuature Chinese ceramic masks

I had forgotten about this little box of miniature masks.  I unearthed today when I was sorting out some cupboards. I have no idea what the faces mean.  They were given to me, many years ago,  by a Chinese post graduate student  studying in Cambridge . He and his wife invited me to  tea and served it in traditional  Chinese style; it was most interesting and enjoyable. .  I did enjoy my time working at Sidney Sussex College meeting students from all over the world.  Happy days!