In most cases metal mosaic tiles will come in the form of a stainless steel capping which is glued on top of a ceramic base. They come in a wide variety of shapes, colours and sizes, usually ranging from as large as 10 x 10cm, down to 1 x 1cm.
304 grade stainless steel is the most common metal for mosaic tiles, and to a lesser extent copper and aluminium. Although 304 is not 306 marine grade stainless steel and not rated for outdoor use, from my own experience I have had a 10 x 10cm test piece sitting outside my back door exposed to the elements for over a year and it is as shiny as the day I put it there (and I live right next to a salt water lake.) I’d be interested to see how long it lasts soaking in salt water.
Cutting Metal Tiles
Mosaic tiles which incorporate metal pieces cannot be cut with a tile scoring tool. It should ideally be cut with a continuous diamond blade electric water cooled saw.
Avoid using an electric saw which is not water cooled as it will leave scorch marks on the stainless steel.
If no water cooled electric saw is available then stainless steel mosaic tiles can also be cut by hand with a ceramic tile hacksaw.