TrailDies.com is a Web site devoted to the study and cataloging of a coin variety type called "design extension." Design extension is a sub-type of the well-known minting process error known as a doubled die. Design extensions first came to the attention of variety coin specialists in the form of "wavy steps" on Lincoln Memorial pennies. Experts who studied these wavy step coins eventually realized that most specimens that exhibited wavy steps also had characteristic "trails" emerging from certain design elements on the pennies, usually from the corners of the letters in E PLURIBUS UNUM or from the columns of the Lincoln Memorial building.
A number of theories have been put forth in an effort to explain these curious marks. The experts who are leading the investigation into the enigma, BJ Neff and Robert Piazza, have studied thousands of coins in an attempt to get to the bottom of the mystery. Their current working hypothesis is that a "design extension" occurs when something goes wrong in the hubbing process during die manufacture at the Mint. Neff and Piazza define "design extension" as "a continuation of one or more design elements on an affected die." The continuations manifest themselves in the form of trails, wavy steps, and other marks that indicate an anomaly during hubbing.
TrailDies.com - A Labor of Love
To be sure, most of the trails, waves, and other marks found by Neff and Piazza are extremely minor, requiring the assistance of strong magnification or even a microscope to see. However, some of the specimens they have cataloged show strong, obvious, and dramatic trails, and it's easy to see why they'd be curious about the cause, especially when they have proved that it is a phenomenon that is happening to the dies rather than the individual coins themselves. Neff and Piazza have cataloged over 1,000 distinct dies that show this design extension, and more than 700 of these dies have been carefully micro-photographed and posted to their Web site, TrailDies.com, as a labor of love for the humble Lincoln Cent and a new type of doubled die mystery that is sure to engage die variety enthusiasts in the search for more specimens. In fact, the design extension variety has already been noted on all other currently minted U.S. coin types, and is expected to be found on certain world coins, as more and more people join the hunt for them.