Fig. 40.—Gloucester, Cathedral, Cloister.
In the matter of construction, fan vaulting differs from any preceding method. Its ribs are all of precisely the same curvature, their length being determined by the position which they occupy, and they are no longer supporting but rather decorative members. The lower portions of some of the vaults still resemble true ribbed vaulting in that the tas-de-charge is used, and also in the fact that the ribs still rise in a single long voussoir from their imposts to the first horizontal ring. But from this point to the crown, the ribs and mouldings are merely carved in relief upon the jointed masonry, which they therefore in no way support. In some fan vaults, as, for example, in Islip’s chapel in Westminster Abbey,[254] and in Gloucester cathedral cloister [(Fig. 40)], the rib is even carved upon the vault masonry for its entire length.
The one structural advantage which the fan vault afforded lay in the fact that it could be built up of practically horizontal courses in a manner to exert very little outward thrust; while the substitution of curved, for straight liernes did away with the awkward angular intersections characteristic of lierne vaulting. Altogether, it is both a clever and beautiful type of vaulting well suited to the builders of the Perpendicular Gothic period, with their fondness for intricate decorative rather than structural problems.
Pendants
Because of its late development, fan vaulting was not extensively used to cover an entire church. Nevertheless, King’s College Chapel at Cambridge (vaulted between 1512 and 1515),[255] and Bath Abbey (cir. 1500-1540),[256] furnish two excellent examples, to which might be added Henry VII’s Chapel at Westminster (cir. 1500-1520).[257] The latter is essentially of fan type, though the fans are in combination with a system of transverse arches and pendants best understood from the photograph and drawing just cited. The vaults in the foregoing churches, do however exhibit minor differences. For example, the transverse arches are practically concealed in the vaults of the naves at Sherborne, and Bath and in the east aisle of Peterborough, while they are prominent in Henry VII’s and King’s College chapels. Moreover, in a number of fan vaults as well as in others of different type, pendant voussoirs or keystones are employed. These are supported by some clever building trick and beautifully carved either as lanterns or reliquaries,—like those of Oxford cathedral choir,[258]—or decorated with rich floral, heraldic, or other designs. Thus they play a rôle which is largely decorative, though one which also marks a very clever building technique.[259]