The half cents of 1804 come in twelve varieties, Cohen 1 through 13. Cohen 3 has been de-listed as an early die state of Cohen 5 (or C5). One of those varieties, C6, shows one of the most striking progression of die states on any modern series.
Die states are distinct, distinguishable differences in condition of a given die caused by any of a number of factors. Those factors commonly include die wear, rust, lapping (commonly called polishing or re-grinding), clashing, or damage. The C6 variety shows two different examples of these actions, both wear and damage.
The obverse die is the famous "spiked-chin" die which was paired with four different reverses for C5 through C8. This same die was the obverse which, before it was damaged, yielded the pairing originally called C3. Since there are no records indicating the cause of the damage, we are left with speculation. One common belief is that the damage was caused when the obverse die was brought into play against a planchet with a bolt lying upon it. On this variety there is no significant deterioration of the obverse die through the entire run.
The reverse die is really where the interesting things happen. Early in its life it was likely damaged which led to significant deterioration of the die with continued striking. It begins as cracks through the tops of a significant amount of the legend and progresses from there.
Die states for this variety have been studied by numerous researchers. The states I will enumerate here are numbered by Manley number, which starts at 1.0 and goes through 12.0. Other numbering schemes were put forth by Breen, Braig, and Katman. Well-known collectors have specialized in this particular coin and contributed significantly to knowledge around this variety and its die states, including Lanny Reinhardt.
This example is earlier than Manley's earliest, his 1.0, which you will see soon. The obverse has been double-struck, most readily visible in front of Liberty's profile. The reverse is, in my opinion, a brockage-maker. That means that it was struck into another, blank planchet which left the circular impression. The diagnostic die cracks for Manley 1.0 can possibly seen extremely faintly between TA and from the rim through the tops of MER. This is only visible at extremely high magnification and is difficult to see, even on this image.
Next is an example of Manley 1.0. This state shows light (but for the large part easily visible to the naked eye) cracks through the tops of UNITED STATES OF AMERICA and the bases of 200, though a few letters and the final zero do get missed. Contrast this with the previous image.
Manley 2.2 shows the cracks having thickened through MER as well as the top of the initial A of AMERICA, the A of STATES, and the fraction. New in this state is the weakening at the top of the letter U.
The obverse of the next coin shows a significant lamination from the lower left through the top. Laminations are caused by improperly-prepared planchets with impurities or gases in them which are expressed at the time of striking. Occasionally, as in this case, flakes of metal will fall off of the coin (see the upright of R). The reverse is an exhibit of Manley die state 2.5, wherein the uprights of U are significantly deteriorated and the top of the A in STATES has a heavy crack on both sides. This is what Gene Braig called the "flying A."
The next example is of Manley 5.0. The indistinctness of the U has expanded to cover the top of the N, and the cracks through MERICA are considerably heavier with a branching crack from the C to the rim. A cud is fully-formed over ME.
Manley 7.0 sees the cud over ME extending through the top left of the C in AMERICA, and the cud over UN is also complete, though it misses on dentil over the right of the N. There is also a retained cud (which still shows some denticles) below 20.
This next gorgeous coin is an example of state 9.0. The dentil over UN which was not consumed in state 7.0 is now included in that cud, and a triangle-shaped cud goes from the left side of the now-heavy crack which goes from the left side of M to the rim through part of the branching crack through the tops of OF.
The area above I of UNITED is beginning to "fill in" (per Lanny Reinhardt) in this coin which would be an extremely early example of Manely state 9.5.
Manley state 10.2 has a complete cud from UNI through 20, as well as from the middle of M through MERICA to the rim. New in this state is the thickening of the crack from the top left of M to the rim.
My example of Manley state 10.5 shows a straight edge-of-strip style rim clip on the obverse, causing some weakness to the obverse strike. The reverse is slightly sharper, and shows the distinct roughly-square gap in the cud which is growing above M.
Finally, something a little different. This isn't a coin at all. It is a construct made by or at the request of Gene Braig to show how he believed the reverse die may have progressed. It also corresponds to Breen's state XVI, which he claimed to have discovered an example of in around 1954, as well as Katman state 10 which that cataloger had not seen. According to Breen, Roger Cohen may have seen or known of an example. No example of this coin or anything close to it is currently known to collectors. They never existed or are now lost. This is almost certainly an electrotype, as the piece itself is exceedingly heavy.
For images please see a followup post, as there seems to be a limit of 20 images in a single post.
For further reference, I recommend "The Half Cent Die State Book" by Ron Manley, "Walter Breen's Encyclopedia of United States Half Cents" by Walter Breen, and "American Half Cents, The 'Little Half Sisters'" by Roger Cohen.
Roll Searching Since July 2007
as a reference) but what really impressed me are the images 
Hybrid Mode
