Not a whole lot of Mount Washington glass was marked. Many of the pieces that were marked were only done so with a paper label. Those paper labels have not stood the test of time. Others were marked with black or gold enamel, which can also easily come off. I would say 90% of the lower end line of Mount Washington was just completely not marked at all. If something is not marked, then you have to rely on the shape and other characteristics of the piece in order to identify it. We have a list here of some of the marks used by Mount Washington Glass Co.