| Popis: |
Different kaolin clay specimen exhibit varying colours after firing depending upon the relative presence of different mineral impurities, physical state of mineral constituents etc. Spectrophotometers used for determining colour values generate many sets of colour data. Interpretation of such colour values is a subjective matter. Increase in darkness, yellowness etc as a consequence of increase in chromophore impurity content in kaolin clay have been shown. However, the inverse of above ie; gradual change in colour values along with gradual change in chromophore impurity content over a realistic range has not been studied. Whether the colour data of kaolin clay after firing can be taken up as a function of impurity content needs to be investigated. Thus, to identify the correlation between kaolin clay impurity content and it's fired colour data the present investigation examined the hypotheses i) The colour development after firing of kaolin clay is an indicator of chromophore impurity content present therein and ii) All the colour variables (L, a, b, ISO2470, redness) constituting a colour data set of pressed kaolin clay specimen after firing will vary in similar manner such that to represent variation in impurity content. The study indicated that the colour values obtained by spectrophotometry of clay specimens after firing represent the chromophore impurity present therein in a less reliable manner. To relatively estimate the quantity of chromophore impurity present in a clay sample from its fired colour, the sample should be mixed with 50% by weight of potash feldspar, pressed in to tablet suitable for colour measurement and fired at or above 1220°C to vitrify. After that the ‘L’, ‘a’ and ‘ISO2470’ values obtained truly represent the chromophore present therein. |
