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1. Introduction

Classically, the two main ways of studying metals and alloys were metallography (the examination of polished and etched surfaces) and cooling curves (looking for discontinuities that indicated some sort of phase change). Both these methods involved considerable skill and experience, and the results were not always unambiguous. The introduction of X-ray diffraction provided a much clearer, simpler and more objective way of investigation.

The methods also led to an understanding of atomic arrangements and so they are more fundamental; they led to the present-day theory of the nature of the solid state, but this article will not be concerned with this subject.

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