Still, M.C.W. Roman Lead Sealings. (University of London, 1995).
PhD dissertation, University College London, Institute of Archaeology.
This thesis is based on a catalogue of c.1800 records, covering over 2000 examples of Roman lead sealings, many previously unpublished. The catalogue is provided with indices of inscriptions and of anepigraphic designs, and subsidiary indices of places, military units, private individuals and emperors mentioned on the sealings. The main part of the thesis commences with a history of the use of lead sealings outside of the Roman period, which is followed by a new typology (the first since c.1900) which puts special emphasis on the use of form as a guide to dating. The next group of chapters examine the evidence for use of the different categories of sealings, i.e. Imperial, Official, Taxation, Provincial, Civic, Military and Miscellaneous. This includes evidence from impressions, form, texture of reverse, association with findspot and any literary references which may help. The next chapter compares distances travelled by similar sealings and looks at the widespread distribution of identical sealings of which the origin is unknown. The first statistical chapter covers imperial sealings. These can be assigned to certain periods and can thus be subjected to the type of analysis usually reserved for coins. The second statistical chapter looks at the division of categories of sealings within each province. The sealings in each category within each province are calculated as percentages of the provincial total and are then compared with an adjusted percentage for that category in the whole of the empire. The final chapter is based on the iconography found in the impressions on the sealings. This includes the styles of imperial portraits, deities, animals, inanimate objects, designs which may come from outside of the empire, similar impressions on other items, epigraphic styles and possible examples of matrices.
Available online: http://discovery.ucl.ac.uk/1317870/
Still's Volume I, Figure 1 (modified for optimal online display) is provided below with a summary description of each type.
1. Two-sided with different sized obverse and reverse resulting in flange around flan.
Uses: Imperial, Provincial, Military, Miscellaneous
Imperial - , 
Provincial - 
Military - virtually all sealings found in Britain (at least) of legions [0390-0423], alae [0444-0453], cohorts [0454-0523], beneficiarii [0524-0526], equites singulares [0527-0528] and pedites singulares [0529-0531]
Miscellaneous - [0678-0679], , , , [0735 -0736]
Date Range: Late 1st century - 4th century
2. Two-sided with various shapes of flan.
Uses: Imperial, Official, Provincial, Civic, Miscellaneous
Imperial - , , , , , , 
Official - [0290-0291]
Provincial - [0314-0315]
Civic - 
Miscellaneous - Numerous records (see Catalogue) but few in terms of percentage of total Miscellaneous category
Date Range: Late 2nd century - 4rth century
This is the most common type of double-sided sealing, if only because it covers so many possible methods of manufacture.
3. Two-sided with squared-off appearance due to having been cut from a lead bar.
Uses: Imperial, Miscellaneous
Imperial - [0011-00141 squared, cut-off chunks and  squared, cut-off
Miscellaneous - 
Date Range: Last half of 4th century (with possible example from 3rd century)
These sealings appear to have been chopped off from a flat bar of lead, had cord holes drilled through them, and then were impressed, probably cold, either with or without boulloteria. In some cases, the hole may have been drilled in the bar prior cutting.
4. Two-sided consisting of two plates, joined by a strip, clipped together.
Cohorts -  and two uninscribed examples mentioned under this entry
Date Range: 3rd century
Roman sealings of this form are extremely rare. Presumably the tool which crushed the two plates together also applied the inscription. The inscription refers to Cohors V Gaiorum who are attested at South Shields (the find spot of the sealing) in the third century. There are collections of similar examples, all from Sicily, which belong to this type but which appear to be either Hellenistic or Byzantine. The style does appear later as a cloth seal, the earliest in the Netherlands in the late thirteenth century and in England from the late fourteenth century (Egan, 1994, 1-2). There are also examples from the seventeenth, eighteenth and nineteenth century (Egan, 1994,95, 99) and perhaps even more recently.
5. One-sided with swelling on blank reverse (sometimes rising from surrounding flan), sometimes with fabric or wood impression on the reverse.
Uses: Imperial, Taxation, Provincial, Civic, Cohorts, Miscellaneous.
Imperial - 
Civic - ?, ?
Miscellaneous - , , , , , 
Imperial - , , [0053-0054], , [00671, 
Taxation - 
Cohorts - 
Miscellaneous - , [0835B], [0837-0838], , , , , , , [1058-1059], , , , , , , , , , , , , , , , [1418-1419], , , , , , , ?
Date Range: Throughout Roman period
This is one of the most common shapes of sealing. There are numerous examples in most categories. The swelling on the reverse of these sealings can take many forms, including rounded, pointed, steep or shallow, since it is usually irregular. Quite often the slope of the swelling does not start from the actual edge of the flan but from a few millimeters inside. Sometimes the swelling can start from the very edge of the flan and be strongly dome-shaped. Sealings of this type must surely have been formed using molten lead at their actual moment of use, rather than being formed as blanks and then used later.
6. One-sided with flat reverse.
Uses: Imperial, Provincial, Civic, Cohorts, Miscellaneous.
Imperial - , [018 1-0182], , , , , 
Provincial - [0320 - 0321]
Civic - , 
Cohorts- , 
Miscellaneous - , , [09401, , , , , , , , , , [1591 - 1592], , , , , , [16931, , , [17681, [1782-1783], , , 
Imperial - 
Provincial - 
Miscellaneous - 
Civic - 
Cohorts - , 
Miscellaneous - , , , , , , , , 
Date Range: Early 1st century - 5th century
7. One-sided rectangular mould-formed bars.
Uses: Imperial; Civic; Miscellaneous
Imperial - , [0192-0193]
Civic - 
Miscellaneous - , 
Date Range: 3rd - 4th century
The regular shape of these sealings and their flat reverses suggest that they were formed in some sort of mould. They may have been used as blanks which were cold-struck with the matrix or they may have been stamped while hot with a die which may have been hinged to the mould or may have been held separately. Some examples were formed in bulk inside a two-halved mould, for example  which bears a seam mark around the edges and the remains of a cut sprue at one end. This also appears to be true for . Record  does not appear to have any string holes but seems to have been attached by a nail which was driven in from the obverse. Only the three Imperial examples can be dated. They all bear the legend 'DN' in one form or another and so can probably be dated to the third - fourth century.
8. One-sided with central nipple on reverse.
Uses: Imperial, Official, Miscellaneous
Imperial - , , 
Official - [0287A]
Miscellaneous - , , ?
Date Range: 3rd century - 4th century
The presence of the central nipple would suggest that the reverses of all of these examples were formed in a mould.
9. One-sided with pedestal-foot projection on reverse.
Legionary - [0439-0441]
Date Range: Early 2nd century - ?
10. One-sided consisting of two plates
Date Range: AD 15-30.
These are apparently the only examples of this form. They are extremely small. These examples are closely dated by their presence in a fort beyond the German frontier which was only occupied for approximately fifteen years.