ISO 489:1999

Plastics — Determination of refractive index

This International Standard specifies two test methods for determining the refractive index of plastics, namely:

Method A: a refractometric method for measuring the refractive index of moulded parts, cast or extruded sheet

or film, by means of a refractometer. It is applicable not only to isotropic transparent, translucent, coloured or

opaque materials but also to anisotropic materials. The method is recommended when great accuracy is

required. It is not applicable to powdered or granulated material.

Method B: an immersion method (making use of the Becke line phenomenon) for determining the refractive

index of powdered or granulated transparent materials by means of a microscope. Monochromatic light should,

in general, be used to avoid dispersion effects. The accuracy of this method is about the same as that of

method A. It is applicable to isotropic translucent, coloured materials but is not applicable to opaque materials

nor to anisotropic materials.

NOTE 1 The refractive index is a fundamental property which can be used for checking purity and composition, for the

identification of materials and for the design of optical parts. The change in refractive index with temperature may give an

indication of transition points of materials.

NOTE 2 The accuracy of method B is approximately the same as that of method A when an experienced operator uses the

method with extreme care (see clause 7).

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