1. J.H. Johnston, R.T. Harper, N. Wiseman, The Controlled Precipitation and Use of Amorphous Silica from Geothermal Fluid or Aqueous Media Having a Silicic Acid Concentration, NZ Patent No 232170/228472, 1990. pp. 105
2. R.T. Harper, J.H. Johnston, S.G. Keyte, T.J. Gresham, The use of geothermal silica to improve newsprint quality at Tasman Pulp & Paper Co. Ltd.: Development of the technology to extract a silica filler from geothermal water, Paper Presented to the APPITA Conference, 1992
3. R.T. Harper, J.H. Johnston, I.A. Thain, An Integrated Approach to Realise Greater Value From High Temperature Geothermal Resources, A New Zealand Example: Proceeding of World Geothermal Congress, Italy, May 1995. 2853–2858
4. J.H. Johnston, R.T. Harper, The Controlled Precipitation of Amorphous Silica from Geothermal Fluid or Other Aqueous Media Containing Silicic Acid, Amorphous Particulate Silica Products Produced Therefrom, and Uses of Such Products, NZ Patent No 245,823, 1996. pp 157
5. J.H. Johnston, R.T. Harper, N. Wiseman, Controlled Precipitation of Amorphous Silica from Geothermal Fluid or Other Aqueous Media Containing Silicic Acid, US Patent No 5,595,717, 57 pps, 1997