PAINT THINNERS – 1
Post 416 –by Gautam Shah
A paint thinner is a very misnomer word. It essentially means nothing that is specific or worthwhile. Yet everyone uses it for many different things and purposes. Few are seeing a great ecological evil. A paint thinner could be a specific single liquid like water, turpentine or spirit or a designed combination of several solvents of natural or petroleum origin. A specific purpose thinner system may also contain other compounds like driers for paints (metallic salts), catalytic agents, retarding (rate of drying) and accelerating compounds, dissolved dyes, preservatives, biocide, lubricants and plasticizers.
A ‘paint thinner’ is used in application of paints, cleaning of paint application utilities like brushes, spray-guns and for cleaning drops and over-sprays. It is also used as de-greasing agent and cleaning of machined components. Thinners are used for diluting many chemical compounds, cleaning body parts and wounds. Thinners are used in agrochemicals, insecticides, textiles, printing inks, oil (both edible and industrial) refining industries, fabric cleaning.
A thinner for paint or coating system, reduces the viscosity of high viscosity materials, dissolves solids, acts as an emulsifier, adjusts the surface tension and encourages ‘wetting’, works as a non mixing carrier and reduces the temperature of exothermic reactions by evaporative cooling.
Film forming substance or the binder defines the thinning or dissolving agents required for purposes like wetting, solution making, suspension forming or dilution. Water has been the most versatile solvent. It is easily available, non toxic and environmentally friendly material. Water as a thinning-diluting or suspending agent, however, has been improvised by addition of agents such as salt, urine, ammonia, soap, sugars, etc. All solvents, except for water, have a toxic effect on organic tissue, biochemical, physiological and neurological side effects.
During the primitive age water was the chief liquid additive to mineral-based powder colourants and ground materials. The property of water making clay for ceramics into plastic form was concurrently known. Water helped spread the colourants evenly over a larger surface. It along with other natural gums and starches improved the bond with the base surface. The gums and starches were hygroscopic materials and would ‘run’ in presence of moisture.
Wax was a heat softening material, and at places natural creosotes was a dark coloured material with binding properties. Natural plant and marine oils provided binding, but were nondrying materials. For early periods of civilization there were no ‘solvents’ available. Presence of ethyl or methyl alcohol in distilled products must have been known. Similarly the pine derivatives, such as pine-oil, terpene and their miscibility with the plant gums, were known by Iron age. Pine-derivatives like pine-oil and terpene, were also miscible with oils.
The need for solvent was partly solved by lowering the viscosity through heating, or by adding emulsified substances like egg whites. Artists used to paint with heavier pastes of paints to prevent ‘running’ but needed to keep the paint ‘green or un-dried’ with use of oil-water emulsions. In other paint systems egg yolk with a little vinegar, emulsions of egg, casein, gum, or glycerine thinned with water, and casein glue with linseed oil, egg yolk, were used to adjust the viscosity and binding qualities.
First true solvent was the terpene oil or turpentine, often called ‘genuine turpentine’ to differentiate it from petroleum turpentine. This material diluted the oils, oils modified with gums, and bodied by boiling, oxidizing or polymerizing. Other substances were the natural distillate alcohols. Alcohols were widely used in Varnishes, Lacquers and French polishes to dilute the natural gums.