If you are interested in looking at a great book on historical
jewelry, check out this book published by the British Museum on
their jewelry collections:
Jewelry 7000 Years: An International History and Illustrated Survey
from the Collections of the British Museum (Hardcover) by Hugh Tait
Here's the link to this book, where it is available as a used book.
It was published a while ago and can only be bought used. You might
try getting it through interlibrary loan first.
It has wonderful photographs from all historical periods, and
includes jewelry from a vast geographical range as well. Once you
have studied the pictures of all that high-karat gold jewelry, and
actually worked with the high-karat gold in your hands, you'll likely
be hooked, and you'll find a way to sell such high-priced pieces.