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Understanding Strike

03-Apr-2010

If you already have a vague idea on grading, you probably know the importance of strike and probably define it as how well the detail was struck up at the time of a coin's strike. While this is an important part of assessing strike, it represents only part of the picture. The grade awarded by strike assesses all parts of a coin's strike. Everything from the centring of the design on the planchet to the effects from contaminants on the planchet during strike. Strike is an important factor in grading mint state coins but is generally overlooked in the circulated grades usually playing only a minor role.

Most dealers will have built up experience on the typical strikes of the coins they deal in, they will be familiar with the orange peel surface characteristic of late Sydney mint strikes, the undetailed and often filled Perth mint strikes and the reflective brilliant surfaces of late Melbourne mint strikes. While experience is important, it is no substitute for ability to independently assess strike, most notably when dealing with foreign coins.

There are several factors that contribute to the quality of a coin's strike:



Unfortunately most dealer descriptions tend to end at either 'weakly struck' or 'well struck' if anything is said at all which isn't much help at arriving at a final grading.

Pressure

Pressure is quite simply, the amount of pressure applied onto the planchet when struck. This affects detail and the metal flow. If you have read my article on lustre, it will be clear how strike pressure affects metal flow, but to summarise, higher pressure strikes form deeper grooves into a coin's surface increasing the radiance of surface reflections.

Die Wear

As a die works through its useful life, it is damaged, details are worn away, it may crack, its mounts will wear allowing it to rotate, shift out of position, etc. While any number of these may be considered by some collectors as collectable errors, from a strict striking point of view, they are faults and adversely affect a coin's strike. A coin struck from a worn die will be less detailed, may show die cracks, die upsets, etc. A fresh die on the other hand will generally pass die polishing striations onto the coin often creating greater contrast with a coin's design.

Contaminants

Throughout a die's useful life, it regularly requires maintenance, often in the form of oil cleaning, acid treating, etc. Often these leave behind residue which, along with other contaminants that might have found their way onto the face of the die, fill the die, or create artifacts on a coin's surface. While again these are often collected as errors, they are an undesirable trait as far as strike quality goes.

How do you assess strike?

The quality of a coin's strike is generally well represented by the reflectivity of a coin's original surfaces. This indicates the pressure (see my article on lustre for an explanation why), but in addition, as a die ages, pressure needs to be dropped to prevent damage to the die so low pressure is also an indication of a later die state. As a die ages contaminants find their way onto a die and in addition the die will obviously wear over time. This however, should not be used as a sole indicator of strike quality and die wear and contaminants should be assessed separately. From 1949 the Melbourne mint trialed the usage of chrome plated dies. These dies, much tougher than standard dies were able to strike coins at much higher pressures without risk of damage, below is a comparison between a threepence struck from chrome plated dies (left) and a threepence struck from standard dies. Note the variance in reflectivity, how the appearance of the 1962 threepence is bolder and more reflective. This indicates that it was struck at a much higher pressure than the 1963, a positive trait.



Die wear is best described as an inverted wear to the insides of the design. While a coin wears on the highest points, dies wear on the sharp edges of design due to the inverted design nature of a working die. This produces poorly defined detail edges on a coin's design, note the base of the wheat stalks in the 1962 threepence. Even though the pressure was high, these points were already worn by the time this coin was struck. Below is a photo of the obverse of that threepence:



Note the two raised lines to the left of the bust, these are most likely light scratches on the face of the die which were passed onto the coin. As these are not particularly common on 1962 threepence, one can only assume that this coin was struck rather late in the die's life. Most peculiar considering high strike pressure but easily explained due to the toughness of the chrome plated die, continuing to allow high strike pressure even late in the die's life. Overall the 1962 would still rate rather high as far as strike goes but is notably not perfect.

Large contaminants are easily measured as grooves in the surface of a coin that pass freely through the design of a coin without raised metal indicating that it is a part of the design on the die, rather than post mint damage. See the incuse line on the reverse of this half sovereign:



This appears to have been caused by a small wire left on the die as the coin was struck, often referred to as strike through errors. These usually indicate poor quality control at the mint but are often collected by coin error collectors.

Contaminants also come in the form of oil or other liquids filling the die such as the penny below:



Note the lettering up the top and how it is incomplete. This is caused by oil residue being left in the incuse devices of a working die and thus affect the raised surfaces of the end product. Again an undesirable quality in a coin's strike, often mistakened for wear accounting for the apparent scarcity of some Perth mint copper coins in mint state.

Application in Grading

How all of these factors add together to form the final grade on strike is up to the collector, I rate them out of 10 as followed:

10: Perfect even brilliant or matte surfaces (such as modern proof or specimen coins)
9: Mostly evenly brilliant surfaces possibly with a hint of minor wear, filling or damage on the die or missing detail due to a central strike weakness but should not be apparent on the coin without close inspection.
8: Generally evenly brilliant surfaces, minor wear, filling or damage permitted on the die or missing detail due to a central strike weakness which may be of a more significant nature but should not be easily detectable without close inspection.
7: Bold detail definitions some minor wear, filling or damage is permitted on the die or detail missing due to a central strike weakness but should not detract from a coin's appearance.
6: Bold detail definitions with evident imperfections in the striking process such as minor die cracking, slight offsets, a slightly off-centre strike, small regions of die fill, or missing detail due to uneven strike pressure.
5: Strong detail definitions, not necessarily with bold definitions but certainly without any noticeable die wear around the important definition points of a coin's design. Minor die cracking is permissible, as are most other strike defects though none should severely detract from coin's appearance.
4: Some strong detail definitions are present though some are filled or worn. Die cracking and other strike imperfections are permissible but most of the coin's design should be present, albeit weak.
3: Indications that the die is nearing the end of its useful life become more apparent with poor overall detail, a dull finish indicative of a low pressure strike, potential porosity of a coin's surface passed from the die, often coined the orange peel effect due to the coin's surface being reminiscent of orange peels.
2: By this stage most dies will already have been withdrawn from use with multiple cracks, die rust present. The coin's detail will be poor with much of the detail missing due to die fill or due to a low pressure strike intended to prolong the use of the die.
1: At this point most of the design will be undetailed and surfaces will be rough and dull due to die rust and a low pressure strike. This will give the coin the appearance of a lower grade coin but the originality of the surfaces can still be a good indicator of grade.
0: By this stage the die will be well beyond its useful life with much of the design missing or undetailed. Surfaces will be rough, the coin will present multiple die cracks and even if mint state, the coin will appear generally undesirable.

These numbers translate to the maximum a coin can grade numerically based on its strike characteristics (just add 60 assuming the coin is mint state). Keep in mind that strike only plays a partial role in a coin's grade and more often than not, other factors will limit a coin's grading further.

What will probably surprise people is how poor the lower grades actually are. The reason being is that these standards must cater for all coins and while Australian coins will at worse receive a 3 for strike, many foreign coins were struck to an even poorer state enabling the necessity for the lower grade points. This is the reason that many collectors believe that American graders are very loose on strike, allowing a coin with obviously poor strike definition into an MS64 grading such as this:



While this may be the worst struck 1937 crown, it's certainly far from being the worst struck coin overall and thus can still make an 4 grading for strike.

I will also add a similar chart for my article on lustre soon which plus this, and in conjunction with another such chart on surface grading, will form an invaluable chart on grading mint state coins.


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