A sculpture is created either by adding material to a core or removing it from a block. In the additive method, the sculptor builds up his work from the inside out in a soft material, generally clay or wax; the clay is then hardened by firing, while the wax is destroyed when the form is cast in bronze. The subtractive method is much more common in the late Middle Ages.
Over half of the sculptures produced in the medieval period were carved from wood . A standing figure was typically cut from a halved section of a tree trunk, clamped horizontally in an adjustable workbench that allowed the block to be rotated. Working from this angle, the sculptor was able to envision the figure in strong foreshortening, much as the viewer would when the finished work was installed above eye level; thus the sculptor could compensate for visual distortions by adjusting proportions and modeling. After marking the contours of the figure on the block with calipers and compasses, he roughed out the form with a variety of tools: two types of axes, curved and straight adzes used in an overhand chopping motion, broad chisels, and mallets. The deeper recesses were created with augers and hand-cranked borers. Various chisels and gouges were used for the elaboration of forms, working from the highest point to the deepest. Certain parts of a figure, such as hands, attributes, and protruding folds of a drapery, were carved separately and attached to the figure with dowels. The backs of figures were normally hollowed out to prevent the wood from cracking as it aged. The carvings were meticulously finished with knives and scrapers, exploiting the contrast between broad, smooth areas and incisive details. Last, decorative patterns were either appliquéd or cut or pressed into the surface with punches. Before a figure left the sculptor’s workshop, the eyes and lips were often tinted.
Equal mastery of wood and stone sculpture is a technical achievement, since the two materials present different qualities . Stone is brittle because of its crystalline structure, while wood is tougher because of its cellular structure. Although stone breaks easily if dropped or struck, it offers greater resistance to precision cutting with a chisel than wood does. The sculptor must therefore combine physical strength with a steady hand, removing material little by little as he works toward the intended form.
Among the most engaging works of the later Middle Ages are carvings in alabaster, a translucent sedimentary stone that varies in color from white to light beige ; . Extremely soft when first quarried, this material allows a high degree of detail in carving. Fastened to a sculptor’s bench, it could be worked with much the same tools as used to carve wood. The stone could be polished to a bright sheen, and was occasionally enhanced with paint and gilding.