In the U.S., imports are regulated by Customs & Border Protection (CBP). From CBP's website:
"For U.S. Customs and Border Protection purposes an antique must be over 100 years of age at the time of importation. Antiques classified under heading 9706 in the Harmonized Tariff Schedule (HTS) are duty-free, provided the importer has proof of the goods' age (i.e. the year of manufacture).
Certain items, namely original artwork, pearls, semi-precious and precious stones, stamps, coins, and collector's pieces (see 9705 for details) should be classified under other provisions of Chapter 97, (or 71 for stones) even if they are antiques.
For more information on duty-free treatment for antiques, please reference the HTS under Heading 9706 (See link below to PDF) and our Informed Compliance Publication for antiques publication (See link below to PDF).
A formal entry is required for antiques imported for resale if the value of the combined shipment is over $2000."
Helpful documents to download:
Harmonized Tariff Schedule under Heading 9706:
Comprehensive CBP Informed Compliance Publication for antiques publication:
If you have additional questions, you'll need to contact CBP directly:
Office of Customs & Border Protection Customer Service Centre: (001) 703 526 4200
Brittany Banta, Vice Consul - Consumer Goods - UKTI USA