The die clash [also called clashed dies] coin error occurs accidentally when the two dies come together in the coining press when no coin blank or planchet is present during the striking process. The result of this is an imprint [or partial incuse image] with elements of designs from the obverse die impressed on the reverse die, and vice verse.

Although the Royal Mint in the past usually makes an effort to clean up these marks or replace the dies, sometimes it continued regular minting using the damage dies with these details impressed onto the following coin planchets.

Some collectors considered clash marks to be common errors, but yet some clash marks are regarded as highly collectible by many Clashed Die Variety and error coin enthusiasts. In the case of the 1½ pence, I think they are more of a sub-variety than an error which are not particularly unusual among the series and can be an interesting method of building a collection, of course every individual has different point of view.

Δ   In this photos of 1½ pence coins, outlined in yellow, on the first specimen [top] there are clash marks on the top from about 10 o'clock to 1 o'clock between the legend and the King's hair [type 1834-1837] and on the second specimen [bottom], from about 10 o'clock to 2 o'clock between the legend and the Queen's hair [type 1834-1862].

This happens because the coin die which struck the coin planchet had a crack or small break in it, which allows metal to flow into the damaged area during striking a coin and that got transferred to the planchet during striking. This appears usually in the form of a small blob or a thin irregular raised line on its surface.

Many times small die cracks fell within accepted tolerances of flaws during coin production at the Royal Mint, but since coin dies though do wear out, need to be replaced when a large crack appears. However in the past, it was a common practice at the Mint to use a certain die until it broke. If the broken die remains in production, more extreme errors can result, including a cud, an unstruck portion of a coin’s surface, among other errors as some remained in production for multiple years, it is difficult to call them non-collectibles as it resulted from intentional recycling of the die.

Since identical either obverses or reverses minted by the same die can not have one or more die breaks in different places on the planchet’s surface [it must be corresponding to the same area on the die where a piece has broken away], such error although most are considered a defect by some collectors, this has proved to me as a key in the process of identifying some varieties in the series since many times, when a couple of dies are supposedly identical, they are not really. 

Perhaps many collectors do not agree with this, but it is fine from my point of view. Some of these errors are collectable, as happens with several coins from the 1½ pence series struck during the reign of William IV [1834-1837], where die cracks are most commonly found in the obverses, while during the reign of Victoria [1838-1862], are most commonly found in the reverses.

Δ   As an example of the preceding explanation, this photos from obverses of two coins of the William IV period & same date. When compare each other, details in both are identical, except any microscopic difference, if any. In the first coin [top], is a die crack from field through 3rd. I of IIII to rim, absent in the second coin [bottom] but in the second coin, from field to dentil next to 2nd. L of GULIELMUS, which does not exist in the first coin. Therefore both coins were struck using two different dies, thus they are two different varieties.

Detective planchets and lamination flaws [same family so to speak] come in all shapes and sizes. Defective planchets are caused by defective sheets from which the planchets are struck. Sheets can be defective for a variety reasons including impurities or debris in the metal used. Often seen on all coin types, minor planchet flaws don't always command a premium price, however, such errors in three halfpence series are scarce, if not rare, and always sought after by the error collector. 

Δ  This 1843 1-1/2 pence coin struck on a defective planchet. It has several reverse die cracks, but it also had a defective or split planchet from center of the coin on both sides, outlined in yellow [first & second images], all the way around to 3 o'clock through the edge [third image],that I believe with little effort this coin could be broken in half. It also has what looks like a triple strike thru the motto REGINA, but I'm not sure because the planchet is so messed up, slightly bended also, that I thought it's possible the coin just didn't strike properly. 

Die rotation refers to the location of the "top" of the coin's image when the coin is turned over. For example, if you look at the obverse of a 1½ pence the Monarch's head right-side up, and then turn the coin over from top to bottom, the crown, wreath and numerals within it, should be right side up on the reverse, which is called "coin alignment."

Nearly all world coins, are struck in one or the other of these proper die alignments. However, die rotation errors are known to exist, where the coin's reverse isn't precisely lined up with the obverse, when one die or another became loose in the coining press, it rotated from its normal orientation or alignment. The 1½ pence is not an exception. Some of them have been found randomly with die rotations ranging from a few degrees off, to a full 180 degrees off, also known as "upright reverse" or "medal alignment". On nearly all medals, the alignment is the opposite. If you turn a medal over from top to bottom, the reverse will be upside down, because it requires that the reverse be right-side up when the piece is turned from side to side [rather than from top to bottom]. The reason for medal alignment being different is that medals are frequently hung on ribbons or chains, and if the medal gets turned over, the wearer wouldn't want his medal to look upside down.

Δ  It is possible to measuring degrees of die rotation of a coin either counter clockwise [CCW] or clockwise [CW] by using this gauge made of plastic first called The Rota-Die, introduced in 1979 by Innovation Enterprises, Inc.

1½ pence coins showing 15 or more degress of rotation misalignment, particularly more often in 1862, are known of the following dates and/or varieties:



Δ  As an example of the preceding explanation, this photos from reverses of two 1½ pence coins, and compare each other using the rota flip. The first specimen [top] has a CCW die rotation of 15° opposed to normal die rotation alignment of the second coin [bottom].

The strike-thru or strike through error term is given to an error observed on a coin where there is an incuse marking on the coin that looks as if there was something on or adhering to the coin surface at striking. This might happen during cleaning or maintenance of the coin press, debris, [which can build up around machinery], made up of oil or grease needed to maintain the presses mechanical activity, metal filings, or some other foreign material etc., may get onto the surface of the die. When this occurs it can fill certain areas of design and prevent those areas from being struck up on the coins the dies are striking.

If a coin is struck though grease then the resulting coin will have the appearance of a missing piece in the design or a poorly struck surface, know as struck through grease filled die. This is often more impressive on a coin when missing important features such as a letter, numerals in the date or even the whole area is obliterated. The effect of a strike through grease may have the appearance that the surface [in that area] has been harshly cleaned or machined down, this is because of the texture of the foreign material and the concave impression it gives to the coin surface.

This specific error that range from minor examples to majors with values ranging from just a few cents over face value to hundreds of dollars, depending in the severity and coin type affected. All 1½ pence coins I have seen with this error had evidence of the most frequent occurrence, where the grease doesn't get anywhere interesting on the coin, and simply obscures or weakens a minor area of the surface, and almost nobody ever notices it. But even all this is really just poor quality control from the mints resulting in poor quality coins rather than collectable error coins, this type of error in a three halfpence is spectacular, then expect a premium price for the coin.

Δ  This are close-ups images of two coins with evidence of strike-thru error, outlined in yellow. In both cases we can see that the reverse was the recipient of most of this activity, while the coin was being struck.

On the first coin [top], the areas closest to the crown and fraction of denomination where the grease first enters the dies is the most affected. If you look closely, you can see a very faint yellowish residue of grease on the surface of the coin, next to the tail of 2 in fraction.

On the second coin [bottom], the reverse got covered with a thin layer near the denomination affecting portions of one of the numbers of the date, but not too dramatically. Other than that, the reverse is very well struck.