Porcelain salvaged from shipwrecks has important documentary value. A shipwreck is a kind of time bubble and we can be sure that all the porcelain in the cargo was loaded at the same time and that all the different types were produced at roughly the same time, too. Almost all Chinese export porcelain was shipped overseas in Chinese junks, East-Indiamen, Arabic vessels, etc. Usually, the porcelain cargo dates the wreck, but sometimes the wreck dates the cargo if the ship's name and the date it sank are known. Research by maritime archaeologists is needed for more details and the historical context. This is why clandestine salvage operations without a proper archaeological survey are regarded as vandalism because important and unique information is lost forever.