Fat over lean

'Fat over lean' refers to the principle, in oil painting

Painting

Painting is the practice of applying paint, pigment, color or other medium to a surface . In art, the term describes both the act and the result, which is called a painting. Paintings may have for their support such surfaces as walls, paper, canvas, wood, glass, lacquer, clay or concrete...

, of applying paint

Paint

Paint is any liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.-History:...

 with a higher oil to pigment ratio

Ratio

A ratio is an expression that compares quantities relative to each other. The most common examples involve two quantities, but any number of quantities can be compared. Ratios are represented mathematically by separating each quantity with a colon – for example, the ratio 2:3, which is read as the...

 ('fat') over paint with a lower oil to pigment ratio ('lean') to ensure a stable paint film.

Oil paint

Oil paint

Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...

 dries at different rates due to the differing siccative properties of the constituent pigment. However, everything else being equal, the higher the oil to pigment ratio, the longer the oil binder will take to oxidize, and the more flexible the paint film will be.

'Fat over lean' refers to the principle, in oil painting

Painting

Painting is the practice of applying paint, pigment, color or other medium to a surface . In art, the term describes both the act and the result, which is called a painting. Paintings may have for their support such surfaces as walls, paper, canvas, wood, glass, lacquer, clay or concrete...

, of applying paint

Paint

Paint is any liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.-History:...

 with a higher oil to pigment ratio

Ratio

A ratio is an expression that compares quantities relative to each other. The most common examples involve two quantities, but any number of quantities can be compared. Ratios are represented mathematically by separating each quantity with a colon – for example, the ratio 2:3, which is read as the...

 ('fat') over paint with a lower oil to pigment ratio ('lean') to ensure a stable paint film.

Oil paint

Oil paint

Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...

 dries at different rates due to the differing siccative properties of the constituent pigment. However, everything else being equal, the higher the oil to pigment ratio, the longer the oil binder will take to oxidize, and the more flexible the paint film will be. Conversely, the lower the oil content, the faster the paint dries, and the more brittle

Brittle

A material is brittle if it is liable to fracture when subjected to stress. That is, it has little tendency to deform before fracture...

 it will be. Ignoring this practice, even in some alla prima painting, may result in a cracked and less durable paint film.

It has been claimed by some paint manufacturers that the 'fat-over-lean' principle can be circumvented by using synthetic, alkyd-based painting media such as Galkyd and Liquin. These media do provide consistent drying times, increase the paint film flexibility, and promote adhesion between paint layers. However, since classical painting media, turpentine, natural resins, and certain plant oils ( linseed

Linseed oil

Linseed oil, also known as "flax seed oil" is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction....

, walnut

Walnut oil

Walnut oil is oil extracted from Persian walnuts.-Culinary use:Walnut oil is edible and is generally used less than other oils in food preparation, often due to high pricing. It is light-coloured and delicate in flavour and scent, with a nutty quality...

 and poppy

Poppyseed oil

Poppyseed oil is oil extracted from the seeds of the opium poppy .The whole seeds of the poppy plant are edible and have been used for cooking since ancient times...

), applied properly have lasted for centuries, some artists choose to avoid synthetic media since their long-term stability is unknown.