They are covered in colorful pieces of broken glass tiles.

VOA: special.2010.05.07

And on the inner wall close to the courtyard actually what you see are some glittering tiles, thats what we call the luminary wall. Each lit rectangle tells about Chinese-American who has been important in American or world history.

VOA: special.2010.03.03

Foam insulation damaged the shuttle's heat tiles during launch, which led to Columbia breaking apart upon re-entry.

VOA: standard.2009.07.16