Most of his works have painted inscriptions showing distinctively shaped letters and numerals .
The earliest portrait of a Scottish sitter recognized as Adam 's work is dated 1622 , though his portrait of Sir William Stewart of Grandtully ( 1567 - 1646 ) is dated 1613 .
Most of Adam 's works have painted inscriptions showing distinctively shaped letters and numerals .
The earliest portrait of a Scottish sitter recognized as Adam 's work is dated 1622 , though his portrait of Sir William Stewart of Grandtully ( 1567 - 1646 ) is dated 1613 .