1. British Plastics, 1965 (September), 564–567.
2. British Patent No. 877,913 (1961), Farbenfabriken Bayer.
3. British Patent No. 1,541,023 (1979) Coal Industry (Patents) Ltd.
4. British Patent No. 1,459,031 (1976) Coal Industry (Patents) Ltd.
5. British Patent No. 1,569,814 (1980) Coal Industry (Patents) Ltd.