Giorgio Blanco
Bruno Santi
Robinson Flagstones
J. G. Robinson
José María Medianero Hernández
British Standards Institution.
Old English Slate Quarries
María Magdalena Radice
Friedrich Wilhelm Noll
B. I. Dagaev
National Slate Association
Ireland. Department of the Environment.
Andrea Botti
Forschungsgesellschaft für das Strassenwesen (Austria). Arbeitsgruppe Steinstrassen und Steinmaterial.
Francesco Gurrieri
Andrea Benedetti
Unknown Author
Ambastone Company