|In spite of the fact that the day something turns 50 years old, and is then referred to as an "antique" and gains an aura of increased value, there are countless exceptions to this "rule". In fact, value is strongly based on the pairing of scarcity (supply) and desirability (demand). For example, there may be millions made of something, but if everyone wants them, their value and subsequent price is high. Similarly, if only a few are made and no one wants them, their value and price are low. Allow me to be more specific.|
A follis (small denomination coin) of Constantine the Great, Emperor of the Roman Empire was struck at many mints between 311-336 AD. Historically, he is credited with legalizing Christianity in the Roman Empire. This coin is quite common, although it is nearly 17 centuries old. You can buy one from an honest dealer in ancients for between $5.00 and $9.00, depending on the grade.
Many U.S. stamp issues from the 1940s and later were collected and held by hopeful individuals planning on using their increased value to pay for their child's college education or to retire on. Nowadays, over half a century later, those stamps, even in perfect condition are so common (so many were made and saved), that their value to a stamp dealer is less than face value. Fortunately, they can still be used to send letters.
I've received several inquiries by e-mail regarding old foreign coins that were saved by some early traveler and how much they were worth. I'm afraid in virtually all cases, the coins are at or very near face value in the country from which they were issued. There might be a very unusual exception where an extreme rarity is found in a dealer's junk box, but for the most part, used foreign coins are practically worthless to most seasoned collectors. And what they won't buy, you can't sell.
The keys to antique items being considered valuable are rarity, quality, and desirability. If there are a lot of them around, if they're of low-quality, or there's not a stable demand, the item will only be valuable to those who own for the sake of nostalgia, or who are collecting for their own joy and knowledge-building. And these individuals are rarer than the antiques they collect.