Abstract: The present invention relates to a process for inducing homogeneous precipitation of a metal oxide, wherein said metal is capable of existing in at least two cationic oxidation states, which process comprises the steps of: i) providing an aqueous solution of a metal in a lower cationic oxidation state; and ii) adding an oxidant capable of oxidising said metal to a higher cationic oxidation state under conditions such that the mixing of said aqueous solution and said oxidant is substantially complete before precipitation of an oxide of said metal in its higher oxidation state occurs.

Abstract: An interferometer (1) is arranged to form a first interference fringe pattern comprising at least ten interference fringes; recording an image of said first interference fringe pattern; perturbing an optical path in the interferometer (1) to form a second interference fringe pattern comprising at least ten interference fringes; and combining an image of said second interference fringe pattern with the recorded image of the first interference fringe pattern to produce a further image comprising a moiré fringe pattern arising from a difference or differences between the first and second interference fringe patterns. The combining step involves subtraction (4) of digital images. Different wavelengths and interferometers are used: Michelson, Mach-Zehnder, Fizeau, Twyman-Green. In this new approach, all the errors of a poor quality, misaligned system are accepted and then eliminated by the combination process, producing a moiré fringe pattern.