An early example of an elongated coin broken die
The 1939-40 World's Fairs were the pinnacle of celebration in the United States. From 1939 through 1940, World's Fairs were held simultaneously in New York and San Francisco. There were many elongated coins produced for both of these Fairs. In the 1981 edition of Yesterday's Elongateds, 80 coins from the New York Fair were documented.
Below are two examples of the coin identified as most similar to NY-WF4-4f. The images have also been inverted to help show additional detail.
Click the picture to zoom (takes up more than a full screen).
The coin on the left has a raised line running from the top center, about even with the top of the Trylon, down through the center, passing the 1939 to the left, then curving over to the right through the Perisphere, running all the way down and touching the "M" in TOMORROW. Because it is raised from the surface of the pressed coin, it is easy to identify as a die break.
The coin on the right is a standard example of a coin pressed on the same die, but much earlier. Of note is the hole that has been drilled in the top, so that the coin could be put on a key ring, necklace, bracelet or the like, which was very standard on early elongated coins.
The two coins were scanned with opposing light, so that the detail can be seen more clearly and the coins compared closely. The initial "K" - likely the engraver's initial, can be seen clearly in the foreground. Close examination of the 1939, placement of the trees, etc. reveals these to be the same coin.
The die break is clearly extremely large, and another with a longer break has not been observed. Some reasons for elongated coin dies breaking are that the die was not sufficiently hardened, that the die was in fact hardened too much, or the die was stressed by a very hard foreign object being rolled through it that caused the die to break.
What is most curious is the squiggly line at the top center of the coin, just above the die break. It is shaped much like a candy cane. Close examination reveals it to be "skip marks" from a drill. If you have ever drilled by hand on metal, you'll know that the drill bit can "skip" if sufficient pressure is not brought to bear.
The "candy cane" at the top is indicative of just exactly this type of drilling.
While there is no definite proof, as these coins were pressed over 67 years ago, it is fun to speculate about the origin of the coin with the die break. Perhaps the roller had pressed many tens of thousands of this very coin. It's likely that he was quite familiar with the feeling of this coin underneath his thumb as he drilled holes for people in their souvenir coins. Maybe he felt the die break for the first time, and the drill skipped as he hesitantly pulled back to examine the coin. Perhaps the coin was in a vise for drilling, and he stopped short as he decided to take a closer look at the coin? We cannot know for certain, but the coin is very likely one of the last if not the exact last coin pressed on this machine!