Many sumerians were skilled at working with this material even though they had to get the raw material by trading with others. what is the material?

Matels like Gold and Silver

Explanation:

The Sumerians were well known for their metalwork, a craft at which they were excellent. Most of the trading done in Ur (Sumerian city-state) as importing happened here. Imported goods hold valuable metals and semi-precious stones such as gold, silver, carnelian and lapis lazuli. Gold maintained for religious functions as well as in serving as personal ornaments, weapons etc.

adopted the practice of proskynesis, a persian court custom that involved bowing down and kissing the hand of others, depending on their rank.