What Holds Up a Clay Figure Before It Is Fired? A Skeleton Inside

Clay, wax and plasticine have no structural strength worth the name, so a standing figure of any size collapses under its own weight, and an outstretched limb droops and falls off. An internal framework of wire, pipe or timber carries that weight, letting the sculptor apply material around it in the confidence that it will stay where it is put. The framework also defines the pose before any modelling begins, since it fixes the position of the spine, the angle of the hips and shoulders and the direction of the limbs, which means the fundamental decisions about the piece are made in wire rather than in clay and are difficult to change afterwards.

Construction varies with the scale and the material being modelled:

• •Aluminium wire for small figures, since it bends by hand and does not rust
• •Steel rod and pipe for larger work, welded or bolted
• •A backing board or baseboard into which the frame is fixed
• •Cross pieces bound at intervals, which stop the clay sliding down
• •Bulking material such as foam or crumpled paper to reduce weight and clay use
• •Pipe fittings that allow limbs to be repositioned during the early stages

The framework that makes the work possible also makes several later operations difficult. Clay shrinks as it dries and the rigid frame inside does not, so a piece left to dry around one cracks and eventually splits apart, which means a clay sculpture built this way cannot simply be dried and fired. The usual answer is to make a mould from the finished clay and cast the piece in another material, which is why so much modelled sculpture exists as bronze or plaster rather than as the original clay. Where firing is intended, the sculptor must use a temporary support removed before drying, or build the piece hollow with internal walls, or cut the finished work apart, hollow it and rejoin it.

Frameworks are not only a working aid, since several materials need permanent internal support in the finished piece. Reinforced plaster and cement sculpture is built around steel or fibre inside it, and the corrosion of that steel decades later is the commonest cause of failure in twentieth century outdoor work, since rusting steel expands and splits the material from within. Large bronze casts are hollow and are supported internally by an armature carrying the weight through the legs or the base. Conservation of historic sculpture frequently involves discovering what is inside it by radiography and deciding whether the original support can be left in place. Modern practice uses stainless steel or non-metallic reinforcement for exactly this reason.

Building the framework requires committing to the proportions and the pose before any surface exists, which is uncomfortable and is also where most of the failures happen. A frame built with the spine too short cannot be corrected once modelling begins, since lengthening it means rebuilding everything. A limb positioned wrongly can be moved only if the joints were made adjustable. The frame must sit well inside the intended surface everywhere, since anywhere it comes close leaves too little material and anywhere it protrudes ruins the surface. Experienced sculptors therefore spend a large proportion of the total time on the frame and on measuring it against the intended figure before any clay is touched.

Modelling materials have no structural strength, so an internal frame of wire or steel carries the weight and fixes the pose before any modelling starts. Clay shrinks around a rigid frame and cracks apart, which is why modelled work is usually moulded and cast rather than fired. The frame must sit well inside the intended surface everywhere, and a mistake in its proportions cannot be corrected once modelling begins.