There are gray earthen wares from Amlash, belonged to the first millennium BC, in Mellat Museum. Amlash is a historical county in Gilan Province (north of Iran) which has lots of antiquities.
Earthen wares of Amlash mostly belonged to seventh, eighth and ninth centuries BC which were found in ancient graves of mountains.
The most prominent hills and ancient cemeteries in Iran that have gray clay such as: Damghan Hills, Gorgan Hills, Tehran Plain, Qeitarieh Cemeteries and etc are located at the north east part of Iran.
Based on studies and results of radio carbon test (carbon 14), it is clear that the gray clays of Hesar Hill and Torang Hill are older than the clays of other parts of Iran.