Titanium Dioxide in Coatings, Undertone

The undertone of a TiO₂ pigment is directly dependent upon its mean particle size and describes the yellow/blue color shift of tinted colors. A TiO₂ pigment with a larger median particle size than the optimum (theoretically 230 nanometers - 0.23 micrometers) will give a yellower undertone. Smaller particle size (lower than optimum) pigments will induce a blue undertone. This tonal shift is only important in colored (tinted white) paints. In white paints undertone has little influence on the color of the paint. Millennium Inorganic Chemicals pigments are controlled to a particle size that is selected to give a neutral undertone. This gives you, the color formulator maximum flexibility in designing the color palette of your tinting system. You are able to obtain both blue and yellow toned shades readily, without interference from the white pigment in the tint base.

Dispersion of the pigment to its optimum is essential to obtaining the correct particle size and hence undertone. Pigments that are not fully dispersed will develop a yellower tone than optimum in the tinted products as the lack of dispersion effectively increases their mean particle size. Dispersion beyond the optimum mean particle size is not possible as it would be necessary to reduce the particle size of the pigment beyond that set during manufacture. This is not possible with normal pigment dispersing equipment.

The color of the paint is only impacted by changes in undertone when the pigment combination contains TiO₂ and colored pigments. Whilst the color of a white paint is modified by a number of factors. The tonal qualities of colored paints are mainly influenced by the undertone of the white and colored pigments used. Thus undertone is not only a property of white pigments, each color pigment has its own undertone properties. Any and all of these factors influence the final color and tonal qualities of tinted paints.

Tinting systems are becoming increasingly common in paint sales worldwide, making it no longer necessary for the paint stockist to hold large volumes of different colored paints. Using a tinting system, the stockist needs only hold a few tint bases and tinters, or colorants, and still have the ability to supply a wide range of colors. Careful control of the color and tint strength of the bases and colorants is essential for the working of such a system. Consistency of undertone and tint strength of the various pigments, including the white for the bases, is absolutely essential.