Modeling chocolate, also called chocolate leather, plastic chocolate or candy clay, is a chocolate paste made by melting chocolate and combining it with corn syrup, glucose syrup, or golden syrup. Primarily used by upscale cakemakers and pâtisseries to add decoration to cakes and pastries, modeling chocolate is formed into a variety of shapes and structures that cannot be easily accomplished with other softer edible materials such as buttercream frosting, marzipan, or fondant. Modeling chocolate can be made from white, dark, semi-sweet, or milk chocolate. Source
Adding water in chocolate is against the basic rules because even the smallest bit of water starts to makes chocolate creamy, and more water turns the chocolate into a greasy paste that’s not very useful. However, if we also add glucose, the result is a smooth plasticine like texture. The issue is that there will be no single recipe that works for every chocolate. Couvertures will need more liquid then compound chocolate. 20 to 25 percent glucose and water mixture will give a reasonable texture depending of the hardness of the chocolate which is called (snap). This paste can be used for coating cakes, making centrepieces look like curved chocolate, modelling figurines and also cutting shapes from rolled sheets.