How do they do this?

This is really quite a crude mosaic - compared with many that you can see in Venice and elsewhere - and yet the face of Mary is so sweet. This capitello is on the side of a church in Castello. It is rather high up, and difficult to take a good photo through the grill. For more mosaics and more capitelli you should visit Churches in Venice (http://www.slowtrav.com/blog/annienc/), not to be confused with The Churches of Venice site, which is really good too (http://www.churchesofvenice.co.uk/).