When the components of an alloy are uniformly distributed throughout the metal, the sample will produce a typical powder photograph. If the metal is `worked' or, in certain cases, cooled, one of the components often `precipitates'. This can be observed on the powder photograph as `spots' where previously there were uniform lines. If the atoms of the alloy `order' (e.g. in -brass) new lines are formed on the powder film--a `super-lattice' is said to be formed. These phenomena are easily observed by photographic X-ray techniques.
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