A method and apparatus for identifying a material type in an article (20; 21), such as wholly or partly transparent bottle of plastic or glass, including, with the aid of a detector station (1-16, 18, 19, 25), irradiating the article with rays from an infrared radiation source (1), detecting rays which have passed through the article non-absorbed, and then carrying out a correlation analysis of such detected rays. The article is made to pass through the detector station (1-16, 18, 19, 25) in a continuous or discontinuous movement. The rays from the radiation source (1) are successively filtered by the filters (10) consisting of wholly or partly transparent materials which have different spectral characteristics. The rays filtered by the filters and non-absorbed by the article are intercepted in order to form a sequence of measured values representing characteristic transmission signatures of the article. A correlation analysis of the signatures is carried out in relation to statistical models in order to determine the material type of the article.
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