Complex sentence: Black wooden pieces are either made of a dark wood such as rosewood, ebony, red sandalwood, or walnut; or they are made of boxwood and stained or painted black, brown, or red.
Split into simpler sentences: Black wooden pieces are either made of a dark wood such as rosewood, ebony, red sandalwood, or walnut. Sometimes they are made of boxwood and stained or painted black, brown, or red.