Q: In the Hall at Balliol is a painting of John de Balliol dressed in knight’s armour [see above]. Given no part of his face is visible, how do you know it is a painting of John de Balliol?
A: The short answer is that it isn’t ‘a painting of John de Balliol’ at all. It was painted about 400 years after John de Balliol’s death – which occurred well before individual portraiture had become an artistic convention.
The undifferenced family crest on the shield (see http://archives.balliol.ox.ac.uk/History/collegearms.asp) clearly denotes a principal armigerous member of the Balliol family, and the date of death inscribed on the pillar at right of the painting clarifies which one is intended. The portraits of his wife Dervorguilla and translator of the Bible in to English and one-time Master of Balliol John Wyclif, also in Hall, are similarly ‘icons’ of their subjects rather than any attempt at likeness.
update May 2013: Now that the Public Catalogue Foundation’s Your Paintings project is available on the BBC website, it is possible to view an image of the Bodleian’s ‘portrait’ (17th century) of Dervorguilla as well. Unfortunately, they have managed to misspell ‘Dervoguilla’ in Balliol’s two listings, so they won’t appear in searches unless you similarly misspell, but you can see all three together here.