A method and apparatus are described for the production of piston castings, and, in particular, a die construction and method of use thereof are described, the die having a crown forming part (18) separable from a skirt forming part (12). In the method, when solidification of the casting occurs to an extent at least enabling the separation of the skirt forming die part therefrom to be allowed, and the die parts (20, 22) are separated, the casting is retained by the crown forming part (18) of the die. After a subsequent process step, such as the solidification of the remainder of the piston casting, and or the cooling of the piston casting by an air blast (64), the solidified piston is removed from the crown forming part of the die. A plurality of crown forming die parts, and a single, common, skirt forming part of the piston casting die, may be provided, together with handling means for the plurality of crown forming die parts and for bringing said die parts consecutively into mating with the skirt forming die part.

Intumescent sheet material having a matrix whose predominant ingredient is an unfired kaolinitic clay comprising ball clay reinforced by inorganic vitreous fibre (for example, mineral wool) contains heat-expandable graphite as intumescent agent and up to 10 percent by weight of an organic binder. It is made by dewatering an aqueous suspension of the aforesaid ingredients in the form of a layer which includes cellulose fibre as web-forming agent.