I have a few brockages and though I didn't set out to have a sub collection of them; I guess that I do now
A brockage occurs when the coin gets stuck to the die and the next strike produces a mirror image on one side of the planchet.
These are fairly common; though reverse brockages are rarer than obverse, because the mint worker could more easily see if the planchet was stuck to the obverse die.
this is a reverse brockage for Gallienus
The reverse is AETERNITAS AVG, Saturn with harpa standing right; PXV in exergue. RIC 606
Partial reverse brockage
Constantine I
A.D. 320
18x19mm 2.3g
CONST-[ANTINVS AVG]; helmeted and cuirassed bust right.
VIRTVS EXERCIT, [Valor of the army] Standard inscribed VOT/XX with captive seated on ground on either side, S-F across fields.
in ex. AQ[P]
RIC VII Aquileia 48
Constantine I
A.D. 318- 320
20x21mm 3.2g
obverse brockage Siscia mint
should have been VICT[ORIAE] LAETAE PRINC PERP reverse
Constantine I
A.D. 320
17mm 3.6g
CONS-TANTINVS AVG; high crested helmet (bowl shaped) and cuirassed bust right.
For reverse see--
VICTORIAE LAET PRINC PERP; two Victories stg., facing one another, together holding shield inscribed VOT PR on altar.
in ex. P [2 captives] L
RIC VII Lyons 79
Obverse brockage
Obverse brockage
This Constantine I brockage has a line under the reverse bust. For some obscure reason, somebody did this to the flan before striking; which is why the bust obscures most of it.
21mm 2.9g
IMP CONSTANTINVS P F AVG
Constantine I
20x21 3.3g
IOVI CONSERVATORI
Siscia
obverse brockage
Constantine I
19x20 3.0
SOLI INVICTO COMITI
Rome
Obverse brockage
Constantinopolis brockage from Trier
15mm 1.8g
Ex 1989 Nether Compton (Dorset) Hoard