The most common wedding gift over the years has been china or some sort of glassware. With this alone a collector can see how tastes in the glassware and the ways that glassware and china have been made have changed.
As a wedding gift only the best types of glassware or china would be given. This means that through the high class marriages a china making or glassware creator could become either famous or a laughingstock. If they became famous their pieces would be too much for a working man, but if their designs were a laughingstock only the working class could afford to get it. Either way their pieces as time marched on could become expensive depending on whose pieces sold well to whom.
Going to auctions, a collector can sometimes find glass made in the United States. This glass is actually a rare find any more. The older the glass, the rarer the find. The same is true for china. If it is an older type, it will be worth more.
One of the things I personally find amazing in chinaware is that it can portray the most common paints for the country it was made in and the time period it was made in. My grandparents received a china set made in Germany for a wedding gift. This set never got used. It wasn't even used for special family get-togethers because of how precious it was to my grandparents. The last time I saw the set, it still was unchipped and fully painted. It looked as though it was newly painted. That was six years ago. They married more than forty years before that. At that point in time, china was made to last.
This could mean any number of things, but when an archeologist digs up a china set made in Japan in a ruins on the Asian continent and it dates to the time of the Vikings (no this has not happened as of yet) it could help piece together some of the past. There is no end to the number of things that one piece of china located in an odd place for the information that has been gathered on it can lead to.
As for china and glassware being a window to the past, it can show some of the unique things that has happened, or it can show materials that we have yet to discover. The most important thing to remember when dealing with any window to the past however is that it is only a window to the past as long as it is available for research and there are people willing to do that research. This research includes a history of ownership for newer pieces and culture diagnosis for older pieces found at a dig site.