Post 492  by Gautam Shah


Thinners are combination of ‘solvents’ whereas a solvent is single liquid material. Thinners and solvents are used for many purposes. These can be categorized in roughly THREE categories: 1 as a solvent for reducing the viscosity, 2 as a diluent an intermediating agent, and 3 as a non active carrier agent.

As a viscosity reduction agent it is used with resins, coating materials, adhesives, etc. As a diluent it is used as an extender medium in thinners to extend thereby reduce the cost of costly solvents. As non active material it is used with pesticides, chemicals to achieve greater spread. Some solvents of very low boiling point temperature are used as carrier for sprays etc. Thinners or solvents are used for cleaning surfaces such as restoration of artwork, removal of oil-grease deposits, removal of moisture from very thin crevices such as electronic circuits.

Distillation of crude oil at different temperatures

One of the earliest needs for a solvent was to reduce the viscosity of wax without warming it with heat. Wax was one of the best and easily available waterproofing material, but required heat for softening, a highly dangerous fire prone processes. Similar problems were encountered while thinning vegetable oils, tallow and other fats. These issues were solved with some of the earliest solvent materials the turpentine and the spirits (crude ethanol-based products from fermentation-distillation processes). Turpentine has been known as: spirit of turpentine, natural turpentine, genuine turpentine, oil of turpentine, wood turpentine and turps.


Turpentine is a steam distillation product from leaves of pine trees which also yields gum turpentine, turpentine oil and colophony (rosin). All these products have been used by artist for artwork and by crafts persons. The primary use of turpentine has been as a solvent for paints. During last century menthol and camphor were produced for turpentine, of this camphor was used for early Nitro-cellulose lacquer (NC Lacquer). Artists preferred distilled Turpentine as paint medium as it was more viscous than white spirit, and for being slow to evaporate. The later property was useful for ‘touching’ the colours, and keep it alive (green or wet) for longer duration. Residues or trace gum rosin in Turpentine prevents fast drying of film and keeps it tacky for along time.


During the last century Genuine Turpentine has been replaced by Mineral Turpentine. Mineral Turpentine is petroleum distillate and is also known as white spirit, petroleum spirits, solvent naphtha. It is a very efficient solvent for oil and alkyd-based paints and varnishes. It is as low cost as Kerosene and so used for cleaning oil-grease from engineering products and other dry-cleaning (non-water cleaning of garments, wools) purposes. Turpentine has very little or no odour, so for paint thinner of domestic use, little terpene oil or genuine turpentine is added as a flavouring agent.

ethanol1Alcohol is produced through fermentation-distillation. The resultant product is Ethyl alcohol (Ethanol). The word Ethyl derives from French word ether, meaning a substance that evaporates fast at room temperature. Alcoholic drinks through fermentation of grapes, berries, honey and rice were produced since 7000 BC. Spirit or ethanol was used to dissolve plant gums. Ethanol is miscible with water and its presence reduces the surface tension of water. Pure ethanol is misused for consumption, so many countries have made it compulsory to denature it adding 5% or more methanol. This is also called methylated spirit. Denatured spirits are used for dissolving gums and shellac to formulate ‘French Polish’ and Lac and rosinated Varnishes. It is also used as cleaning agent.

Kerosene is chiefly used as a fuel. There are commercial and superior grades available. It has very strong solvent properties. In far off regions where Mineral turpentine is not available, Kerosene is used as oil paint solvent.

Naphtha sold as Camp-fuel

Naphtha is a flammable liquid mixture consisting of hydrocarbons, and it is very similar to kerosene or gasoline. It is a feed material for fertilizer and chemical plants. It is used for cleaning(flushing out) petroleum product tankers and as a tool machine cleaning solvent.

Gasoline is basically a fuel product, but is used for removing grease, tars and waxes from tools, parts and equipments. It is not used for paints.

Water is universal solvent. Water was used for water-based coatings produced from gums, casein, egg-whites etc. and with cementious compounds like lime, gypsum, etc. Water emulsified, polymer paints are able to meet the ecological concerns for VOC (Volatile organic compounds are organic chemicals that has a high vapour pressure at ordinary room temperature).


Acetone is a simplest ketone and called mother of solvents. It is colourless and flammable liquid utilized as an important constituent of lacquer thinner, nail polish remover and grease-oil cleansing. In restoration and conservation practices acetone is often used to clean dirt, soot and grime and old varnishes from paintings and furniture.

Olivia Boteler Porter before and after restoration – removal of yellowing due to dirt and ageing

Methyl ethyl ketone (MEK) is an industrial solvent which is easily miscible with water. It is used as thinner solvent and as a remover-softener of stubborn paints.

Carbon tetra-chloride fire extinguisher 1930

Carbon tetra-chloride is also known as tetrachloromethane, carbon tet (cleaning industry), Halon-104 (firefighting) and Refrigerant-10 (HVACR). It was very popular cleaning agent for amateur electronics people. It is a colourless liquid with a sweet smell detectable at low levels. It is no longer preferred as a solvent or cleaning fluid.

 Sistine Chapel, the prophet Daniel before and after Restoration

>> A decision was made that all of the shadowy layer of animal glue and “lamp black”, all of the wax, and all of the over-painted areas were contamination of one sort or another: smoke deposits, earlier restoration attempts, and painted definition by later restorers in an attempt to enliven the appearance of the work. Based on this decision, according to Arguimbau’s critical reading of the restoration data that have been provided, the chemists of the restoration team decided upon a SOLVENT that would effectively STRIP the ceiling down to its paint-impregnated plaster.





Post 423 ⇒   by Gautam Shah 


A Paint Thinner nominally changes a material’s solid phase into a liquid phase and heavier liquid into low viscosity liquid. Thinners act by dissolving, suspending the solids and by intervening into viscous liquids.

Paints, Thinners

A thinner is a mix of different solvents that act as a thinning compound, suspending agent and a diluting material. A thinner is also conceived as accelerator or retarder of film formation of a coating. Thinners are used for cleaning of lubricants, machine cutting fluids, coolant materials, greases, waxes, etc. Thinners are used as stripping agent of dry or wet coatings (paint remover). A thinner sometimes may not strip a film of coating, but softens by affecting some of the constituents (through wetting, etching, etc.) of the film. Rest of the stripping act is accomplished with other chemicals, heat softening, singeing, mechanical stripping, scrapping or grinding.


Viscosity of a coating medium can be adjusted by including a low viscosity medium into a high viscosity material or by solvents and diluents. Solvents dissolve by entering the inter-molecular space and changing the intermolecular forces. Diluents by themselves do not enter the inter-molecular spaces but extend the action of a solvent as a liquid to liquid-phase. Often in a multi medium formulation ‘one material that acts as a solvent, to a particular medium, may act as a diluent for the other medium’.

Air brush spray nozzle

Solvents and diluents both increase the fluidity of a coating medium. The fluidity of a coating medium is important for applications (spray, brush, etc.), flow or levelling properties, nature of drying and ‘curing’ of the film. Very high fluidity may not mean very low viscosity. Very thinned down coating material leads to separation of solids (like pigments) from liquids (resins, solvents, etc.) Excessively thinned down coating, on drying produces porous film (a film with marked solvent escape pores). Too much thinning often creates non-opaque or patchy (in terms of colourants) film. Solvents also affect the inter-molecular structure of resins affect their interlinking or polymerization, and thus the quality of the film.


Solvents and diluents are added during the manufacture and also prior to application. For the later purpose, a well proportioned an economic blend of solvents and diluents, suitable for specific categories of coatings are marketed as Thinner or Reducer.

paint-brushes-500x500-250x250Thinning solvents included in a coating material, encourage separation and towards the gravity settlement of solids on storage. Nowadays thixotropic compounds are added to water based coatings (such as Plastic or Latex paints). These compounds create a false setting (thickening of liquid mass into a viscous paste), and with little stirring, the coating material gains the original consistency.

Majority of Plastic (or Latex paint as in USA) are water based system, though very small quantity of solvent do exist in them

Constituents of thinners are nominally low boiling point temperature solvents. These evaporate at a faster rate but are affected by the temperature, moisture, movements of air, and the application process. In nominal weather, 25 ° C and 40% humidity, thinner evaporates at an average rate, but in hot weather thinner leaves the coating film before it has time to flow and level out. In case of moist weather (raining periods) the moisture in the air gets trapped in the film and cause blushes or whitish spots. This can be corrected by using retarder additive or slow drying thinner.

Spray Gun formulations require special thinners

Coating applications require special thinner formulation. French polishes and lacquer coatings applied by rubbing pads need very thinned down and slowly evaporating thinner. Brush application of coatings needs film levelling time, high fluidity without reducing the viscosity. Spraying with compressed air creates cooling and moisture condensation and so prescribed quality of thinners must be used. Spraying by airbrushing (thin-narrow and a fine nozzle) for delicate work, need fast evaporating solvents.




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.

Kathakali Dancers make up Kerala India

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.

Painters Turpentine Oil

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.

Paint Viscosity measuring Ford Cup

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.

Linseed oil in paints

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.

Turpene sourcing

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.

Mineral Turpentine

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.


SOLVENTS and THINNERS for coatings

SOLVENTS and THINNERS for coatings

Post 320 ⇒   by Gautam Shah 


Thinners are specific mixtures of different solvents to achieve desired viscosity for the film forming constituents of a coating system. Solvents are liquids that have power of dissolving or formulation with something.

Viscosity of a medium can be adjusted by including a low viscosity medium into a high viscosity material, or by solvents and diluents. Solvents dissolve by entering the inter-molecular space and changing the intermolecular forces. Diluents are non dissolving low viscosity substances, do not enter the inter-molecular spaces but extend the action of a solvent as a liquid to liquid-phase. Often in a multi medium formulation, one material that acts as a solvent to a particular medium, may act as a dilutent for the other medium. Solvents and diluents both increase the fluidity of a medium.


Various thinning media for oil paint –by Ellywa – Own work. Licensed under CC BY-SA 4.0 via Wikimedia Commons –

The solution of the film forming substances of a coating helps in manufacturing and application processes. Solvents or thinners are also required to clean up tools (brushes) and equipments (spray nozzles and containers) of application. These are also used for removal of patches, over-sprays and body parts.

Solvents convert resin and polymer molecules into smaller clusters, and it is a process of separating the molecules. In solution, the molecules of solute and the solvents are dispersed into each other.

Solvents on evaporation help in formation of a solid film. The coating may be deposited, and solvent evaporates to form a solid film (non-convertible system). Alternatively the coating undergoes one or many processes of chemical conversion (such as oxidation, chemical reaction on application of heat or catalyst reaction), while solvents get evaporated (convertible system).


Most solvents, including the most versatile one the water, evaporate at some temperature. There are two classes of solvents: Hydrocarbon (Petroleum) solvents and Chemical or oxygenated solvents, though these terms are overlapping due to complex process of manufacturing. Hydrocarbon solvents theoretically have only Carbon and Hydrogen but other substances such as Sulphur and heavy metals may be present as trace elements.

Coating formulations are in consideration of Solvents’ cost, flameability and the environmental effects. The solvent-power or solvency is very important aspect. The formulation must achieve a viscosity that is correct for manufacturing or application processes with a minimum amount of solvent. For a coating formulator, another important aspect is the rate of evaporation of solvent. If a solvent evaporates too rapidly, the applied coating will not get sufficient time to level out. Faster evaporation also induces early start for cross linking, and may seal the face, trapping part of the solvent. In spraying a fast evaporating solvent hinders even spray and may cause condensation of water around spraying nozzle and sprayed surface.

Thinners are mix of solvents and other carriers or non-solvent material. Thinners are formulated and proposed by the coating manufacturer, as competent authority they know what forms the coating. Often Thinners of different qualities are suggested such as for application and for cleaning of tools, equipments, patches and over-sprays. Some even provide specific thinners or special additives for monsoon seasons to counter effect of excess moisture and condensation.

For the later purpose, a well proportioned an economic blend of solvents and diluents, suitable for specific categories of coatings are marketed as Thinner or Reducer.

Hydrocarbon cracking Lab plant


Following categories of solvents are used in coatings:

  • Aliphatic hydrocarbons: white spirit (mineral turpentine), kerosene (superior and fuel grade)
  • Aromatic hydrocarbons: benzene, toluene, xylene
  • Alcohols: methanol, ethanol, butanol, isopropanol
  • Chlorinated hydrocarbons: carbon tetrachloride
  • Ketone: acetone, methyl ethyl ketone (MEK), methyl iso-butyl ketone
  • Esters: methyl acetate, ethyl acetate, butyl acetate
  • Ethers: methyl cellulose, cello-solve, cello-solve acetate
  • Terpene: turpentine (genuine), di-pentene, pine oils


by Gautam Shah ➔

Coatings are thin surfacing. A coating comes into being mainly through a phase-change of a material. At pre-application-stage a coating material is in various phases such as solid, liquid or vapour, or a combination thereof like: suspension, solution, dispersion, emulsion, thermoplastic compound, thixotropic compound, etc. During application it changes to a Liquid phase, but once applied, it settles down to a heavier phase, usually (but not necessarily) a Solid phase.

Coatings are not exactly considered to be adhered-finishes, because the coating film is formed and (mainly) bonded through a lower to higher phase conversion process.

Coating is a thin Surface Finishing Technique. A coating system has Four main components.

1. Film forming substances

2. Solvents and Diluents

3. Pigments and Extenders

4. Other additives

Film forming substances are the prime materials of a coating system. Even if other components are not present, a coating (Clear coating) can still be created. Most of the film forming substances are in liquid form or convert to a liquid phase just prior to application. Film forming substances provide a film that binds all the ingredients, and also develop inter-facial adhesion between the coating and the substrate.

Solvents and diluents, impart solubility to specific film forming substances, allow dispersion and adjust the viscosity.

Pigments are chief colourants to coloured coatings. In some clear as well as coloured coatings, Dyes (dispersed or dissolved) are added to provide specific tinge (staining) to the coatings. Other colourants include opacifiers, whitening agents, fluorescent phosphorescence agents. These besides providing colour, impart transparency translucency, opacity, fluorescence, phosphorescent and luminance to the film. Extenders or fillers are low refractivity materials, usually white, but not necessarily. These are added to provide bulk to the coating, economise the use of pigments.

Additives help in manufacturing, storing, applying, drying and maintenance of a coating. These include surfactant, anti skin agents, wrinkle agents, dryers (metallic compounds that helps in polymerization of resins), thixotropic agents, foaming and de-foaming agents, catalysts, odour suppressants, mildewcide, insecticide, fungicide, plasticizers, anti setting agents, etc.

A clear coating (often called Varnish) has no pigments or extenders. For a specific tinge (transparent staining) dyes or very low proportion of pigments are used.

Surface treatments: Coatings are generally capable of forming a film on the relevant surface. But to receive a coating, the surface may require some modification or treatment. Surface treatments form a very important section of coating technology. Surface treatments are specific for the surface to be coated, such as cleaning, roughening, smoothening, etching, etc., or moisture proofing, rust inhibiting, barriers, static arresters, etc. Other surface treatments are designed to facilitate the application or deposition of the surface forming component and its setting or drying.

Coatings are deposited on objects by many different techniques and in variety of conditions. Common coatings are applied at normal environmental conditions. However, high end coatings require conditions that are usually unavailable at construction sites such as exact environment and controlled application, drying and handling techniques.