The 1857/5 overdate half sovereign

Probably one of the lesser known Sydney mint varieties, the 1857/5 overdate half sovereign was first catalogued in the early 1980s in Spink Australia sale 3 (lot 318), ex the Moran Collection and appeared later in Noble Numismatics auction 65 in November 2000.

The Moran Collection 1857/5 overdate - image ex Noble Numismatics (enlarged 3x)
Recently we uncovered a second example, found in an 1857 PCGS slab as XF45, ex the Reserve Bank of Australia and is only the second known example of this overdate.

Our 1857/5 overdate (enlarged 3x)
A few key similarities between the two:

Traces of the centre of a '5' in the opening of the '7' the end of a 5 sticking out the right side of the 7 and the top-right tip of the 5 protruding up the right of the '7'.
A well detailed obverse strike
Dense obverse rim (unclear in our photo as the outer edge is concealed slightly by the slab though is very prominent to the naked eye)
Central strike weakness (particularly the 'R' of 'AUSTRALIA')

While overdating was common practice during the era, the only 1855 dated coin with the wreathed bust, or Type II obverse, was the pattern, so it would suggest that this overdate was produced by the recycled pattern die of 1855.

While it's clear there is a '5' underneath the '7', some confusion comes in as the '1' doesn't match the '1' of the 1855 pattern. This can only be explained by two possibilities.

A thicker '1', as seen in most business strikes was re-punched to prevent die wear and filling to allow the die to strike commercial quantities.
The '7' was prepared from a re-cut '5' punch and struck onto a new die.

Both of these possibilities were suggested by Nobles when they auctioned the first coin however in close comparison with the 1855 pattern, it's clear that the rest of of the design, most notably the rims match perfectly, the rims being distinct from any other business strike 1857 I've seen (except the Moran Collection overdate obviously), though some legend positioning varies between the pattern and the overdate on some letters, though it seems that they too were re-entered, most notably the first 'A' in 'BRITANNIAR' still shows the original 'A' slightly offset which positions correctly with the 1855 pattern.

Note how the 'A' is doubled - it would seem that many letters and digits were re-entered to prepare the die for commercial striking as the thin lettering used with proofs and patterns is easily worn or filled when striking the large quantities required for a commercial production.

One most notable characteristic is the central strike weakness - a central strike weakness indicates that the die had insufficient concavity relative to the strike pressure. This is a common characteristic of circulation issues struck from proofs dies, most notable on the 1934 threepence and 1927 Canberra florins - ever wondered why genuinely proof-like Canberra florins are always undetailed on the steps to the parliament house? This is because proof dies are polished flat to produce the mirror fields and to avoid damaging the proof coin with the high pressure strike, while circulation issues are struck with a slightly concave die to ensure central detail is clear even at the lower pressures required to extend the working life of the die. When a proof die is used to strike a coin at typical circulation strike pressures, the centre of the coin is always less detailed. Half Sovereign collectors will recognise this central weakness on 1866 Sydney mint half sovereigns that have a dense rim as they too were struck from recycled proof dies.

An circulated 1866 half sovereign from recycled proof dies (enlarged 3x)
Notice how strong the obverse rim is (concealed slightly as the coin is in a slab) yet how undetailed the central strike is - this probably isn't such a good example as the coin is already quite worn and the dies at quite a late state with some evidence of cracking in the obverse legends, though the effect of re-using proof dies is still evident. Something of interest though is that again much of the legends have been re-entered (for example the 'NN' in 'BRITANNIAR').

While it's clear that this overdate was prepared from recycled 1855 pattern dies, one should remember that recycling proof dies and overdating was common practice in the era as the preparation of dies was a complex and expensive matter up until the early 1880s. Despite this, rarity is to be expected considering the rarity of the host coins. While only two known examples of the 1857/5 overdate have surfaced, it should be noted as the lack of awareness of this overdate (despite being first referenced in the early 1980s), has stopped many collectors from inspecting their own 1857s for traces of the '5'. Certainly something to look out for.