Blank patents were warrants to survey land for grants that had blank spaces to be filled in later with the description of the land. They were issued by colonial land office officials for their own convenience, since blank patents freed them from having to appear in person to sign each patent individually. The receiver of the blank patent subsequently wrote a description of the land he desired. This gave the individual a claim to a specific piece of property while allowing him to avoid paying taxes until the land was actually surveyed and recorded.
Predictably, untaxed land held under blank patents became a cause of concern to royal officials. In North Carolina, corrupt use of patents was an issue of considerable controversy in the 1720s and 1730s.
DocSouth, UNC Libraries: http://docsouth.unc.edu/csr/index.html/document/csr04-0113 
1 January 2006 | Powell, William S.