There are some stamps in the world that are so rare they are priceless, but what makes a stamp rare in the first place?
Rare treasures and new King Charles III stamp on display at The Postal Museum, News
World's Rarest Stamp Now on Display at National Postal Museum
Wealthy Still Investing In Stamps Amid Overall Slide in Value - Financial Poise
Rarities and Special Holdings
The Six Most Valuable US Postal Stamps That Sell For Up To, 48% OFF
British guiana stamp hi-res stock photography and images - Alamy
World's rarest stamps - The Postal Museum
Why Collectors Fall Head Over Heels for the 'Inverted Jenny' Stamp, At the Smithsonian
The Six Most Valuable US Postal Stamps That Sell For Up To, 48% OFF
Collectible postage stamps - Antique