Oil Painting Mediums; Linseed Oils part 2

Why Use Oil as an Oil Painting Medium

Oil paints in their purest form are made with ground pigment and oil.  Therefore oil is a superb and highly compatible medium.though oil paint can be used directly out of the tube as is (and this is a fine way to paint), there are numerous oil mediums that oil painters can use.  This post discusses the difference between the various types of linseed oil.

What is the Difference Between Types of Linseed Oil

Through their manufacturing methods, the properties of linseed oils can be manipulated : Thickness, Color, Drying Time, Handling and Paint Film Strength.  Choosing a form of linseed oil depends on the desired use.

Linseed Oil

Linseed Oil is produced from the seed of the flax plant.  It dries slowly by oxidation and remains workable or "open" for a long time.  This can be very beneficial to the oil painter.  Once it is dry it can not be reversed.  Linseed oil is an excellent paint binder and medium, and excellent drier forming a strong paint film.  Straight linseed oil as your medium is a time honored choice.  Use less oil in layers closest to canvas and use more oil in the top layers.

Cold-Pressed Linseed Oil

Cold-pressed linseed oil is linseed oil in it's purest state.  Raw flax seeds or linseeds are crushed without the use of heat.  Because this is a low yield process, Cold-pressed linseed oil is a more expensive form of linseed oil.  Although there is some debate, paints made with cold pressed linseed oil are thought to have superior film strength, handling and brilliance to paints made with refined oils.

Alkali Refined Linseed Oil

Flax seeds are processed with use of heat via steam.  The heated seed are pressed and linseed and waste products are produced.  These waste products called mucilage or foots are removed through a refining process.  Sulfuric acid is used to treat the steam-treated, pressed linseed oil which destroys the waste products.  The acid is then neutralized with an alkali.  This alkali-refined linseed oil is a neutral, acid free oil and is is an inexpensive alternative to cold pressed linseed oil.  Less expensive high quality paints with high pigment content can be made with alkali-refined linseed oil.

Refined Linseed Oil

This is the same as alkali refined linseed oil.

Steam Pressed Linseed Oil

This is also the same as alkali refined linseed oil.

Sun-Thickened Linseed Oil

Sun-thickened linseed oil is the choice for using linseed oil as a painting medium during the painting process.  Sun-thickened linseed oil is made by mixing equal amounts of linseed oil and water and then left exposed to sunlight for several weeks.  Exposure to the sun lightens the oil by bleaching and partially oxidizes the oil.  Better results are obtained using this thicker bodied form;  It is a superb viscous medium that leaves texture and brushstrokes on the canvas and because it is partially oxidized and is therefore a faster drier than either cold-pressed or alkali refined linseed oil.  The lighter color and partial oxidation is also thought to reduce the yellowing of paint later compared to cold-pressed linseed oil and alkali-refined linseed oil.

Stand Oil

Similar to sun-thickened linseed oil, stand oil uses heat to create a bodied medium.  Linseed oil is heated at 550° F for at least 12 hours in an airtight oxygen-free container.  This causes the stand oil to polymerize rather than oxidize due to the absence of oxygen.  The result is a viscous medium that does not leave texture or brushstrokes and is superb for used when glazing.  It has a very strong paint film that resists cracking when dry.  I love to use stand oil in my glazing recipe that is damar varnish, stand oil, and mineral spirits.

Superb Oil Paint Medium Technique Using Linseed Oil

1. With paint thinned with mineral spirits (or turpentine) paint first layer onto gessoed canvas or panel and let dry if desired.
2. With paint straight from tube or lightly thinned with stand oil or sun-thickened linseed oil, paint next layers and let dry if desired.
3. With paint thinned only with stand oil or sun-thickened linseed oil, paint final layers.

The above method generally not only maintains a "Fat over Lean" concept but also allows a full bodied layered painting technique improving depth and textural brilliance.  This method dries faster than using regular linseed oils, but still dries slowly.