The proof five dollar coinage of 1907 through 1909 provides quite an object lesson in the evolution of Mint technology and consumer tastes. The 1907 Liberty Head proof, last of the series, was produced in a mostly brilliant or "semibrilliant" proof format that was introduced in 1902; as a result, most proof gold from 1902-1907 lacks much cameo contrast--half eagles or otherwise.
The 1908 gold coins of the new Bela Lyon Pratt and Augustus Saint-Gaudens designs were launched with a new "matte" proof format that was all the rage in European mints of the era. The Robert Loewinger reference, Proof Gold Coinage of the United States, offers this:
"The [matte proof] process originally started in Belgium and was popularized in the Paris Mint. The finish was applied after striking and was made by sandblasting the coins at different forces and speeds with different sizes of grains of sand. Also pickling the coins in a weak acid was another technique that was used on these coins after striking."
We are unsure how widespread the "pickling" was, but the sandblasting was a well-known, widespread Mint technique that produced a granular (sometimes fine, sometimes coarser), usually dark, subdued finish to the product, a function of the lack of normally reflective surfaces. The matte proof coins of 1908 are usually dark, brownish-gold to olive-brown, and they were extremely unpopular with collectors accustomed to a more brilliant finish.
The Mint in 1909 reverted to a lighter Roman or satin finish for proof gold. The updated Akers Handbook offers these thoughts:
"The proof 1909 introduced the Roman Gold proofing method in the Indian Half Eagle series, although at least one specimen was prepared using the dark matte finish of 1908. Despite having brighter, flashier surfaces than the proof 1908, the proof 1909 still failed to gain wide acceptance among the contemporary public The Mint melted many examples at year's end. Interestingly, even though most survivors present as overall smooth, the issue has the lowest average grade in the entire proof Indian Half Eagle series."
A PR67 piece is being offering in the current 2010 October Stamford Coinfest Signature US Coin Auction #1145, and is one of the nicest survivors of the proof 1909 half eagle mintage, recorded as 78 pieces. It is one of six so graded at NGC, with but two coins finer.