In most cases, a postmark or postal cancellation offers a very accurate estimate of an item’s age. Postcards were typically purchased and mailed immediately, perhaps on the same day, or at least within a few days, when the sender had a moment to update their travels. Postcard with cancellations are not very mysterious in that regard.
However, determining the date of an antique postcard can be difficult if the postcard had never been postmarked. In many cases, postcards were simply purchased as travel souvenirs, destined only for photo albums, and were never mailed. Unless the original owner made some sort of note on the back, the age of these postcards will likely be difficult for a novice to estimate.
Postcard collectors rely upon a handful of postcard eras to determine the age of a postcard, and while these eras do not cover the entirety of all postcards, they will answer the question for about 90% of the postcards you will encounter.
Undivided Backs and Private Mailing Cards (1901-1907)
Prior to 1907, the US Postal Service did not allow communication on the backs of postcards; this area was reserved for the mailing address only. Any communications were limited to the front of the postcard, which is why most early postcards feature a small margin for writing on the front. Postcards from this era are referred to as “undivided back” postcards, because there was no need to allocate an area for the message and address on the back. They are very easy to identify.
Notice the postcard below from Coney Island. The message area is the right margin, and the reverse is used exclusively for the address:
Divided Back Era (1907 – 1915)
In March 1907, Congress passed an act that allowed privately produced postcards to bear messages on the left half of the card’s back. This law ushered in the Divided Back Era, which still exists today. However, within the realm of postcard collecting, “divided back” cards do not classify all cards produced after 1907, even though all of these cards technically feature divided backs. Rather, the Divided Back Era applies to cards produced between 1907 and 1915 only.
Although the Divided Back Era spans just a few years, this era was the heyday of postcard production, and millions of postcards have survived from these early days. Because of the vast quantity of product, most postcards from the Divided Back Era are not necessarily valuable, despite being well over a century old. (Similarly, the green 1-cent Benjamin Franklin stamps that adorn most of these cards are rarely valuable either; there are still millions of these stamps in the world.) Among all eras of postcards, the valuable cards are limited to compelling subjects and uncommon views. Age is virtually meaningless.
White Border Era (1915-1930)
Between 1915 and 1930, many postcards began to feature a common look, which was essentially a white border with an Akzidenz-Grotesk-style font (a precursor to Helvetica), either in proper case or all caps. Keep in mind, many postcards produced between the years 1915 and 1930 do not feature white borders, and thus the era does not have a strict, cut-and-dry definition. Postcards from this era featured many different looks and designs. The key idea is that enough cards shared a similar look to brand an era.
Common lore alleges that the white borders were a cost-saving measure for wartime, although the borders also allowed some marginal leeway when the cards were cut from large sheets. Below is a classic example of a White Border Era postcard:
Linen Era (1930-1945)
Of all the postcard eras, the Linen Era is easily the most defined. Linen postcards are characterized by their textured fronts, which helped to produce postcards with strikingly vivid colors. One of the largest manufacturers of linen postcards, the Curt Teich Company, also featured serial numbers that pinpoint the exact year of production. An exhaustive guide to the Teich serial numbers can be found on the Toronto Postcard Club site.