Paint Technology D. Indumathi, The Institute of Mathematical Sciences, Chennai All of you would have surely made drawings with paints. Water colours, poster paints, shiny colours that glow in the dark: all are equally fascinating to children and adults alike. Have you ever wondered how colours are produced? How water colours make a huge mess and then wash off neatly and cleanly, without leaving a trace, while fabric paint stays for ever? Apart from being used in art work, paint has many commercial uses, such as in preventing erosion, controlling temperature, etc. The colour in paint comes from various pigments that can be natural in origin. Varnish and shellac are paints without pigment. They are normally used as a protective coat. A binder or resin is added to allow the paint to be coated as a filmy layer. As the name suggests, the binder binds the pigments together through adhesion. The consistency of paint can be changed using a solvent. This may even evaporate off after drying. If the solvent is water, you get a water-colour paint which washes off easily. Others are oil-based paints. If varnish is added to oil-based paints, you get enamel paints that dry out with a very hard and glossy finish. The paint must satisfy various requirements. For example, it must stick to the surface that is being painted. If it simply peels off, that is no use. So the adhesion property must be just right. Sometimes a primer or a preparatory coating is put on first. This not only improves the adhesion of the final coat of paint to the surface, but also increases the life of the paint. So there are numerous technologies involved in paint production. One is the colour, and choice of pigment. The other is the binder and solvent then of course, there are numerous ways of actually applying the paint: either by hand or brush or even mechanically. Also, it should retain its properties even when it is hot or cold: automobiles, for instance, are exposed to extremes of heat and cold. In fact, some technologies exist that change the colour of the paint depending on temperature. An amusing example is that of a baby's spoon that turns white when dipped into very hot food. This way, the parent can ensure that the temperature of the food is correct without having to taste the food! A more serious and useful example are photochromic paints and coatings. These contain dyes that change their structure when the film is exposed to UV light, and so they change color. These materials are used to make eyeglasses. Also, it is obvious that the requirements for paint quality depend on where it is going to be used. The paint used inside houses is not so susceptible to rusting as those used for automobiles, ships and aircraft. On the other hand, paint used inside houses and for household equipment must be stylish and eye-catching. In short, there is a lot more to paint than meets the eye. All that lies below the (painted) surface is the subject matter that is called paint technology.