Why stop-motion animators love clay that never dries out
Leave a lump of ordinary pottery clay out and it hardens as its water evaporates. Oil-based modelling clay does not, because oil stays put. That simple difference keeps it soft for years, lets it be reused endlessly, and made it a favourite of stop-motion animators, who must nudge their characters into a new pose for every frame.
Modelling clay is really a loose family of squishy materials with very different recipes. The traditional kind is ceramic clay, a water-based mix of clay minerals that is fired at high heat to become terracotta, earthenware, stoneware or porcelain. Oil-based clays combine oils and waxes with clay minerals. They cannot be fired, so nothing made from them is a ceramic, and they do not dissolve in water. Warmth thins the oil and softens the clay, while cooling stiffens it, so sculptors can adjust how it handles simply by changing its temperature.
Several of the best-known names began as trademarks. Plastilin was patented in Germany by Franz Kolb in 1880, developed further by Claude Chavant in 1892 and trademarked in 1927. In England, William Harbutt of Bathampton invented Plasticine in 1897. Roma Plastilina, sold by Sculpture House, follows a formula its maker says is a century old, but it contains sulfur, which stops some moulding compounds from setting, so copying its sculptures can be awkward. Because oil-based clay takes fine detail, sculptors often use it for originals that are then moulded and cast.
Polymer clay, despite the name, usually contains no clay minerals at all. It stays workable until it is baked at around 130 degrees Celsius, roughly 15 minutes for every 6 millimetres of thickness, and it barely shrinks or changes shape as it cures. Artists, hobbyists and children use it, and animators like it for the same frame-by-frame reason as oil clays.
Paper clay adds a small amount of processed cellulose fibre to ordinary clay. The fibres make the dried material stronger and let dry pieces be joined to wet or dry ones. It air-dries light and firm for dolls and crafts, and in a kiln the paper simply burns away, leaving the clay behind.
Source: Modelling clay
