followed by The Cathedral Builders in England in 1905, An Account of English Medieval Figure-Sculpture in 1912, which provided an exhaustive account of figurative sculpture from the 7th –to the 16th Century for the first time. A History of Gothic Art in England made Prior's scholastic reputation and contributed to his appointment as Slade Professor of Fine Art at Cambridge University in 1905. Stained glass In 1889 he developed Prior's glass, also known as Prior's Early English glass, a slab glass which is similar to the "luminosity and varied colouring of early medieval glass." It was made by blowing glass into a rectilinear box and then cutting off the sides. This yielded flat panes of uneven thickness, often streaked with colour. Whereas the prevailing style of glass relied on meticulous draughtsmanship and line control to create rich backgrounds of flat surface decoration such as gothic mouldings or foliage, the new glass could be used to create backgrounds with a more abstract pattern, as in the St Pancras roll of honour, or combined with lead alone to create bold and dramatic effects such as the wings of the four archangels at St Andrew's, Chippenham. Education Prior first became involved in architectural education during the debate over the professionalisation of architectural practice in the 1890s. The protest against examination and registration was launched by the Art Workers Guild, whose members believed, quite correctly, that RIBA wished to establish itself as the sole arbiter of the profession culminating in the publication of a collection of essays Architecture: A Profession or an Art in 1892, to which Prior contributed a chapter criticising the common use of "hirelings" to do the architect's work. In the same year Prior, amongst others resigned from the RIBA. As a result of the controversy members of the Guild became very interested in architectural education. The Architectural Association established a School of Handicraft and Design to extend its training scheme. It had been criticised for being too geared to the RIBA's examination system. Prior was one of the architect-visitors who drew up projects and gave the "crits". He became increasingly interested in education, giving lectures at various conferences, to the RIBA and schools of design. Moves were instigated to establish a School of Architecture at Cambridge in 1907. The syndicate seeking the establishment of the school included Prior's old headmaster Dr H.M. Butler, who was by then Dean of Trinity