In the Irish form of crozier the front is flat, and shaped like an oval shield. This is often moveable, disclosing a hollow behind it, which was almost certainly used as a reliquary.[73] The materials of which the pastoral staff was made were very diverse. The stick was of wood, usually some precious wood, such as cedar, cypress, or ebony. This wood was often gilt or overlaid with silver plates. In the twelfth century the staff was shod with iron and surmounted with a knob of crystal, above which the crook proper was attached. The crook-head of the Irish crozier was of bronze; that of the other form generally of carved ivory. When the process of elaboration was felt in this as in all the other sacerdotal ornaments, the stick as well as the head was often carved from ivory, and either gilt or silvered heavily, and set with precious stones. Beneath the crook were often niches or shrines, containing figures of saints. The bronze Irish crozier was decorated with the marvellous interlacing knots and bands which are the special glory of early Irish Christian art. On the flat front is often to be seen a plain cross, at the centre of which is a setting for a precious stone, and in each quarter an interlacing band. In the volute form of crozier a different style of ornamentation was adopted; the surface was not ornamented, but the head was carved into solid forms; in the centre of the volute was usually represented some sacred person or scene, real or legendary, or else some symbolical device or conventional patterns. It is hard to say which of these two forms of crozier is the better from an aesthetic point of view. The graceful curve of the volute certainly compares favourably with the somewhat stiff outline of the Irish crozier; but the feebleness of even the best mediaeval attempts at representing the human figure in miniature considerably detracts from the artistic value of the volute crozier when a human figure is introduced; while, on the other hand, the incomparable excellence of the Irish metal-workers transformed the U-shaped crozier into an object of great beauty. The lines of the knots are always faultlessly executed, and the ornamentation is invariably in good taste.[74] The following copy of the Lincoln Inventory of pastoral staves (1536) illustrates some of the points already noticed. It also indicates that the head and staff of the crozier were separable, and, when stored in the vestry, kept apart from one another: 'In primis a hede of one busshopes staffe of sylver and gylte wᵗ one knop and perles & other stones havyng a Image of owʳ savyowʳ of the one syde and a Image of sent John Baptiste of the other syde wanting xxj stones & perles wᵗ one bose [boss] and one sokett weyng xviij unces. 'Item one other hede of a staffe copoʳ & gylte. 'Item a staffe ordend for one of the seyd hedes the wyche ys ornate wᵗ stones sylver and gylte and iij circles, a boute the staffe sylver and gylte wantyng vij stones.