Many copies made are fairly small and one problem has always been, how to finish the edges? Unless you already have a frame or you place one on after you need a way to cover up the edge of the board and tesserae.
One thing I use is a epoxy putty called 'Milliput' in the UK. It can be a bit messy and time consuming and you need to be careful you do not get any on the surface of the mosaic. It does though give a nice finish as if you have set the mosaic into a terracotta base.
There are other colours available but I usually got for the terracotta finish.