The first step in the investigation of archaeometallurgical slag is the identification and macro-analysis of slag in the field. Physical properties of slag such as shape, colour, porosity and even smell are used to make a primary classification to ensure representative samples from slag heaps are obtained for future micro-analysis.
For example, tap slag usually has a wrinkled upper face and a flat lower face due to contact with soil.
Furthermore, the macro-analysis of slag heaps can prove an estimated total weight which in turn can be used to determine the scale of production at a particular smelting location.