However, a detailed history of the invention of the Mackintosh was published by Schurer. The essence of Macintosh's process was the sandwiching of an impermeable layer of a solution of rubber in naphtha between two layers of fabric. The naphtha was distilled from coal tar, with the Bonnington Chemical Works being a major supplier. Syme did not propose the sandwich idea and his paper did not mention waterproofing. Waterproofing garments with rubber was an old idea, and was practised in pre-Columbian times by Aztecs, who impregnated fabric with latex. Later, French scientists made balloons gas-tight (and incidentally, impermeable) by impregnating fabric with rubber dissolved in turpentine, but this solvent was not satisfactory for making apparel.