Skin
The surface, either of a mould or casting, is designated as the skin by most foundrymen. The aim of a conscientious moulder is to produce castings exactly like the model or pattern, externally and internally; free from blown and shrunk holes, no cold-shuts, and to present a clean surface or skin--the last being to him the chief desideratum. To obtain the latter quality in the resultant casting many schemes are practised in order that the intensely hot and liquid metal may be prevented from penetrating beyond the skin of the mould; the chief agent employed for this end being carbon, which is contained in some proportion in nearly all the facings made. See FACING; FACING-SAND; GRAPHITE.