Determining the age of a wristwatch based on luminous numerals, dial and case

The luminosity can be used to determine when a vintage watch was manufactured
The first thing you can look for to determine when a vintage watch was made is the lume, if present. Historically, watches were illuminated with radium. This was banned in the U.S. in 1968 because its radioactivity posed safety concerns. Many manufacturers switched to tritium around 1963. Tritium became the industry standard until Luminova and similar compounds were introduced in the late 1990s. If you can determine which of the three you're looking at, you'll have a rough guide: pre-1960s, 1960s to late 1990s, or late 1990s or later.

So, how do you tell? Well, sometimes it's on the dial. Tritium-illuminated dials are usually marked with "T," "T<25," "3H," or similar markings to clearly indicate that they're free of radium. If nothing similar is present, there's a good chance it's either radium or a modern compound.

You can also look at the color of the lume. Tritium tends to yellow over time, while radium typically ages in more pumpkin and brown tones. Modern compounds don't age at all and mostly stay white or pale green. These are generalizations with countless exceptions, but they help provide a rough starting point. Radium also tends to damage the dial and hands over time. Its gamma radiation eats away at the varnish. If a watch sits unused for a long time, the radiation can even leave ghostly shadows on the dial from the luminous hands hovering above. You'll also sometimes see dials that have faded toward the center, where the hands are more visible.

The hands are classic, but the tiger's eye dial, modern font and TV-shaped case clearly point to the 1970s

The 1940s, for example, were characterized by cathedral hands, sword hands, syringe hands, and leaf hands. These leaf hands persisted into the 1950s, but dauphine hands also enjoyed enormous popularity. In the 1960s, things became easier, as the baton hands were subject to considerable strain.

In the 1970s, more and more manufacturers began experimenting with new shapes. This led to rounded shapes and non-traditional handsets.

The dial can be used to determine when a vintage watch was made
Of course, a watch's hands don't stand alone. They're equipped with a dial, which provides another way to identify when a watch was produced. Again, I'm generalizing quite broadly here, but there are certain styles that can be associated with different decades.

In the 1940s, for example, most dials still featured printed numbers. Sector dials also enjoyed great popularity. The 1950s saw a rapid increase in the number of applied indices. Many are quite ornate, such as the arrowhead indices on Omega Constellations from the 1950s.

Similar to the hands, dials also became simpler in the 1960s. Stick/baton indices were commonplace, resulting in a cleaner, more modern aesthetic. The 1970s saw a shift in dial printing. The typical pointed serifs were increasingly omitted in favor of simpler sans-serif fonts. Experimentation with surfaces and materials also increased. Vignetted dials, sunburst finishes, stone dials, and colors were all the rage. Be careful, though; these had already emerged in the 1960s.

The case reveals when a vintage watch was made
The case can provide several clues as to when a vintage watch was manufactured. First, there's the material. In the 1930s and 1940s, many watches had chrome-plated cases. Chrome plating continued into the 1950s. So, if you have a case with flaking chrome, it—again, generalizing—dates from the 1950s or earlier. Staybrite is another material that was particularly popular in the 1930s and 1960s.

In the 1940s, lugs with fixed strap rods (also called "fixed lugs") were popular. By the 1950s, most manufacturers had switched to some form of removable spring bar. In the 1930s and 1960s, lugs tended to shift from ornate to simple. Classic cornes de vache (cow horn) lugs tend to date from the 1950s or earlier, while square, slender lugs are more indicative of the 1960s. Likewise, very small crowns were fashionable on dress watches in the 1960s, partly because fewer people were relying on manual winding. The large but flat crowns that were common in the 1930s and 1940s largely disappeared in favor of more tubular crowns with smaller diameters.

A C-shaped case is another clear indication of a watch from the 1970s

Until the late 1960s, watchmakers labeled waterproof cases as "waterproof." Over time, this term was replaced by "water-resistant," since no case is completely waterproof. This is another element with very vague boundaries, but it's unlikely you'll find a "waterproof" watch from the 1970s.

Lugs made of Corne de Vache, leaf hands, printed numerals and a flat crown – most likely from the 1940s

source: replicawatches.com, Charles Martin