I posted this in the other thread also-
I learned this when I thought I had a matte proof-
Matte proof Lincoln cents were made by:
1. new, unhardened dies were sandblasted.
2. the dies were hardened normally.
3. these dies were used in an hydraulic medal press to stamp the coin (one blow from the press).
All dies started out with flat rims and nearly square junctions between field and rimes or lettering, but only the medal press could exert enough pressure to force this fully into the coin planchet.
This process produced the distinctive surface on Lincoln cents 1909-1916 and 1913-1916
Buffalo nickel proofs.
The matte surface did not wear well and dies had to be replaced when the surface smoothed out - probably after a few hundred pieces were struck. (Old, mirror surface proof dies could be repolished and put back in the medal press.)
The Coiner or an assistant examined all proof coins and removed substandard pieces. Pieces that were defective (clips, off-center, multiple strikes) were destroyed; pieces that were substandard but still good coin were tossed into the regular production bins and entered circulation. Mint totals are for the number of pieces accepted by the Coiner (as in the Guide Book), not the quantity sold (except in a few instances where that quantity is known).
Matte proofs can be very deceptive, so follow the advice in Lange's book and have suspect pieces examined by someone with considerable experience.