Cwiertnia, Elke; Ailes, Adrian; Dryburgh, Paul (2019). "Analysis of the Materiality of Royal and Governmental Seals of England with a Focus on the Great Seals (1100–1300): Methodology and Findings". In Whatley, Laura J. (ed.). A Companion to Seals in the Middle Ages. Leiden: Brill. p.32. doi:10.1163/9789004391444. ISBN978-900439144-4. LCCN2018052096. OCLC1060183703.
Cwiertnia, Elke; Ailes, Adrian; Dryburgh, Paul (2019). "Analysis of the Materiality of Royal and Governmental Seals of England with a Focus on the Great Seals (1100–1300): Methodology and Findings". In Whatley, Laura J. (ed.). A Companion to Seals in the Middle Ages. Leiden: Brill. p.32. doi:10.1163/9789004391444. ISBN978-900439144-4. LCCN2018052096. OCLC1060183703.
Cwiertnia, Elke; Ailes, Adrian; Dryburgh, Paul (2019). "Analysis of the Materiality of Royal and Governmental Seals of England with a Focus on the Great Seals (1100–1300): Methodology and Findings". In Whatley, Laura J. (ed.). A Companion to Seals in the Middle Ages. Leiden: Brill. p.32. doi:10.1163/9789004391444. ISBN978-900439144-4. LCCN2018052096. OCLC1060183703.