18:51 Farthing real variety or start of a simple cracked die.

[absence of uniformity]

If you look at the bottom image you can see the faint line of the die crack. The coin was listed/sold as having a colon.

I'm aware a variety is listed for the 1851 Farthing with a purported colon.

Looks like the beginnings of a die crack rather than a colon to me.

 

[absence of uniformity]

[Coinery]

I agree, almost certainly connected with the die crack!

[Paddy]

Could be they drilled a small hole in the die to limit the crack. It is a well known technique to drill a small hole at the end of a crack as it reduces the stress at the tip and so makes it less likely the crack will propagate further.

[absence of uniformity]

1 hour ago, Coinery said:

I agree, almost certainly connected with the die crack!

Both coins are missing the serifs on the B of BRITANNIAR.

[absence of uniformity]

56 minutes ago, Paddy said:

Could be they drilled a small hole in the die to limit the crack. It is a well known technique to drill a small hole at the end of a crack as it reduces the stress at the tip and so makes it less likely the crack will propagate further.

Interesting, do you think the images show that progression? A crack formed, two holes drilled and then the die deteriorated further to show the pronounced crack we see in the first image.

[absence of uniformity]

I just noticed the following; 

https://aboutfarthings.co.uk/catalogue/farthing-varieties/

"Obverse 2e Die Fault resembles colon between 8 & 5 in Datal Figures (Image shows early stage of flaw, advanced stage can be seen in the enlarged image"

I saw a coin listed as having a colon and when looking at other 1851 farthings I noticed the example with the crack, aboutfarthings.co.uk has it spot on.

Edited 11 hours ago by absence of uniformity

[Paddy]

10 hours ago, absence of uniformity said:

Interesting, do you think the images show that progression? A crack formed, two holes drilled and then the die deteriorated further to show the pronounced crack we see in the first image.

I cannot say definitely that is the case, but it certainly seems a possibility. I suppose the other way would be if parts of the die were fragile and broke off around the nascent crack, but I don't think the metal used in the dies was usually that brittle.