Thursday, June 23, 2011


            It might seem at first sight that the examination of white surfaces is merely a special application of the general methods of measurement of colours and that and of the instruments previously described would be satisfactory . It is a curious fact however that the colour of almost white substances is very difficult to measure accurately and consistently with such instruments . The difficulty lies in the eye of the observer and not in the sensitivity of the instrument .
         Very little work has been published upon the variation of sensitivity of the eye with the proportion of white present in a colour but it has been established that the neater a colour approaches white the more insensitive the human eye becomes to changes both in the actual colour (i e hue ) and in the amount of white present (i e the depth of the colour ).