Since the early 1970s, the U.S. Mint has intentionally frosted the
recesses of proof dies, ensuring that the corresponding raised
elements of every coin would have a “cameo” appearance.
This frosting actually constitutes intentional damage to what were
originally sharply defined features. Under a microscope, the frosted
elements look indistinct compared to an early die state circulation
strike or a Proof coin produced before 1971.
Methods of ‘frosting’
Intentional frosting was originally applied to a Proof die by
sandblasting the entire surface and then polishing the field portion
of the die face to a mirror finish (Coin World, Sept. 14,
2009). The frosted recesses of the die face lie below the plane of the
field and are thus protected from polishing. Chemical etching of the
die face and striking the die against a gritty emery disc are other
techniques that were occasionally used to create a frosted surface.
Traditional methods of frosting and polishing dies occasionally
led to mistakes. Sometimes a die was polished too aggressively,
leading to thinned, tapered or undulating letters and numbers
(Collectors’ Clearinghouse, Feb. 21, 2011). Sometimes the polishing
was uneven, leading to wavy fields (Collectors’ Clearinghouse, June
30, 2008). In one case a distinct step was produced (Feb. 14, 2011).
In the last few years, pinpoint, computer-controlled laser etching
of the recessed elements has replaced the traditional methods. In this
process, frosting becomes the last step of die preparation (Coin
World, Sept. 14, 2009). This technique also yields the occasional
mistake. Offset frosting and misplaced islands of frosting have been
observed (Feb. 21, 2011).
New Hampshire quarter oddity
Dale Stokes recently sent me a Proof 2000-S New Hampshire quarter
dollar with a frosting mishap that I’ve never previously encountered.
It involves the label OLD MAN OF THE MOUNTAIN, which appears in incuse
letters within the eponymous (and now collapsed) rock formation. OLD
MAN, OF THE and MOUNTAIN are arranged in three lines.
In Stokes’ coin, each line is surrounded by a precisely ruled,
tight-fitting block of very dense frosting (see photos). The density
of microscopic bumps that compose the frosting is greater than
elsewhere on the rock face. Stokes sent me two comparison Proof sets,
and their New Hampshire quarter dollars showed no difference in
frosting density across the rock face (see photos above).
In 2000, the traditional methods of frosting were still being
used, so I presume that polishing of the Proof field was the last step
in preparing the die that struck Stokes’ coin. The incuse letters of
OLD MAN OF THE MOUNTAIN are polished just like the field.
The edges of the blocks of dense frosting conform precisely to the
outer edges of the incuse letters. On the left side of the first two
lines, the dense frosting ends at the outer margin of the two O’s that
begin each line. Such precision suggests the use of a stencil to guide
the frosting process.
Matter of speculation
Why a stencil might have been used on this die, and why the
frosting density should be different in this area, is a matter of speculation.
The design of the New Hampshire quarter dollar does present unique
challenges when it comes to frosting and polishing. The mountainside
is riddled with cracks, crevices, and cavities, some of which are
quite deep. The cavities on the coin are, of course, generated by
features that rise up from a larger basin in the die face. While I do
not have the equipment to take precise depth measurements, it seems to
me that the deepest cavities approach or match the depth of the incuse
letters they surround. This could pose a problem if the polishing tool
removed the tops of these raised features and left the floors of the
deepest cavities mirror smooth.
To prevent such an accident from occurring, a multistep process
may have been used to frost the die. Or perhaps an accident such as I
described did occur, and this represents a repair job. Beyond these
broad conjectures, I cannot speculate.
One interesting and perhaps relevant observation concerns the
floors of the incuse letters in the anomalous quarter dollar. In most
of the letters, the mirror-like finish is marred by sparsely
distributed specks of frosting. Neither of the two normal coins shows
this. It is perhaps another indication that something went wrong in
the production of this Proof die.
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