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Product Profiles: Thinners for Oil Painting

Thinners are volatile liquids added to paint to reduce viscosity, increase fluidity and dilute color. A thinner might be used alone or as an ingredient of a painting medium. They are also used to make varnishes from natural and synthetic resin.

When thinning with solvents alone, it's important not to overdilute paint, as too much solvent can break down the viscosity of the paint vehicle, leaving resulting mixtures underbound with weak adhesion and reduced film strength. A good rule of thumb is to reduce the viscosity of oil paint no thinner than heavy cream. If a thinner, runnier consistency is desired, a painting medium should be used instead so binding strength is preserved.

Above all else, when working with solvents it's important to follow package directions for safe use. This includes avoiding sources of ignition, working in a well ventilated area and working to minimize skin contact. Depending on the type and volume of thinners used, protective equipment may also be needed.

Turpentine

The traditional solvent Turpentine is a fastevaporating, clear liquid distilled from sap, wood or pulp derived from conifers. Pure Gum Spirits of Turpentine is distilled from tapped pine resin. Sulphite Turpentine is produced as a by-product of the kraft paper process, and wood Turpentine is distilled from stumps and wood chips.

Pure Gum Spirits of Turpentine is regarded as the best for general oil painting purposes, as it helps support drying better than other solvents. All types of turpentine are suitable for thinning paint and making damar varnish.

Despite the fact that turpentine is derived from natural sources, long-term exposure is associated with some health consequences, including allergy-type sensitivity. For this reason, we recommend that artists use odorless mineral spirits for rinsing brushes, and reserve turpentine for thinning colors and making mediums and varnishes.

Mineral Spirits

Mineral Spirits is a water-clear petroleum distillate that can be used for thinning paints, for rinsing brushes, and can be combined with oils and varnishes to make painting mediums.

Products sold as "paint thinner" are usually mineral spirits. The best types for painting are sold as "odorless" or "low odor" because they have been refined to remove aromatic compunds and oily residues that might interfere with drying.

Mineral Spirits should not be used as a turpentine substitute for making damar varnish, as it will not completely dissolve the resin. Some synthetic varnishes can be made with Odorless Mineral Spirits, including some acrylic and styrene-based resins.

Artists should avoid hardware store products sold as "turpentine substitute". These petroleum-derived thinners are generally not nearly pure or clean enough for use in the studio.

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