Here are some references for my students about the fat over lean discussion…..
R&F Handmade paints site
A SIMPLE EXPLANATION First of all, fat over lean refers only to oil painting and not to any other medium. It is a rule of traditional oil painting whereby fat colors (those with high oil content) should be laid over lean colors (those with low oil content). The reasons for this are: • Lean colors are less flexible and can crack when applied over fat colors during the drying process, and • Fat colors can dry to a glossy surface that is difficult for another paint layer to adhere to. HOW DO I KNOW THE OIL CONTENT OF A COLOR? The answer is a little confusing. Manufacturers don’t list the oil content of their colors. Nor do some of the artists’ handbooks. And the handbooks that do contradict each other on several colors. So, while it helps to know which colors are very fat and which colors are very lean, there are a number of variables that make it difficult to know the oil content of every color [see page 2]. At the end of this technical sheet is a list of R&F colors, in the order of lean to fat. It is based on the pigment manufacturers’ specifications and on the way we formulate and mill our paint. Note that other brands of oil paint may vary from this. Note also that if you add a medium to your paint you are changing the oil content.
HOW IMPORTANT IS THE RULE OF FAT OVER LEAN? The lack of specific oil content numbers does not make the rule unimportant. The rule still should be understood. But the good news is that the fat over lean rule is not as rigid as it sounds. Part of the answer depends on your method of painting. Here are points to keep in mind: • Fat over lean pertains to the traditional technique of building up layers of paint after each lower layer has dried. If you are painting wet into wet, the fat over lean rule is of little or no importance. • Fat over lean is most important when you are applying thick layers of paint. If you apply a lean color over a thick layer of fat color, that upper layer can crack. • If you add an oil medium (such as linseed oil or stand oil) to your paint, you are making the paint fatter. This is a way to compensate for the fact that you may not know the oil content of a color.
LIST OF FAT & LEAN COLORS In R&F Pigment Sticks VERY LEAN: Cobalt Green, Cerulean Blue, Neutral White, Mars Violet, Titanium-Zinc White, Jaune Brillant, Brilliant Yellow, Dianthus Pink, Naples Yellow, Azure Blue, Cadmium Orange. LEAN: Turquoise Blue, Chromium Oxide Green, Cadmium Yellows & Reds, Mars Orange, Red, & Black, Cobalt Violets, Cobalt Yellow, King’s Blue, Veronese Green, Manganese Violet, Neutral Grey Pale & Lt.. AVERAGE: Warm Pink, Siennas, Umbers, Indigo, Courbet Green, Ultramarine Blue & Violet, Cobalt Blue & Turquoise, Graphite, Cadmium Greens, Neutral Grey Med. & Dp., Ivory Black, Prussian Blue, Mars Yellows, Viridian, Payne’s Grey. FAT: Iridescent Colors, Warm Rose, Sanguine Earths, Sepia, Green Earth. VERY FAT: Brown Pink, Alizarin Crimson, Phthalo colors, Quinacridone Magenta, Rose Madder. SUPER FAT: Lamp Black, Intense Carbon Black
LIST OF FAST & SLOW DRIERS Here are the R&F colors grouped according to their drying rates. These may differ slightly from those of tube oil colors because of varying amounts of wax content. The drying range is based on paint thickness and absorbency of the surface painted on. VERY FAST(1-4 days): Umbers, Cobalt Yellow, Indigo, Neutral Greys. FAST (2-10 days): Cadmium Green, Cerulean Blue, Cobalt Blue, Cobalt Green Light, Cobalt Turquoise, Cobalt Violet Dp., Courbet Green, Manganese Violet, Neutral White, Payne’s Grey, Phthalo Green, Prussian Blue, Sanguine Earths, Siennas, Viridian. AVERAGE (6-17 days): Brown Pink, Cadmium Green Pale, Cadmium Lemon, Cadmium Yellow Lt. & Med., Green Earth, Iridescent Pearl & Pewter, King’s Blue, Mars Yellow Dp., Mars Orange, Mars Violet, Mars Black, Sepia, Titanium-Zinc White, Turquoise Blue, Ultramarine Violet, Veronese Green. SLOW (7-27 days): Alizarin Crimson, Azure Blue, Dianthus Pink, Iridescent Silver, German Silver, Brass, Gold, Copper, Bronze, Ivory Black, Mars Yellow Lt., Mars Red, Phthalo Blue, Phthalo Turquoise, Rose Madder, Warm Rose. VERY SLOW (10-50 days): Brilliant Yellow Extra Pale, Cadmium Orange, Cadmium Yellow Dp., Cadmium Reds, Chromium Oxide Green, Cobalt Violet Lt. Graphite Grey, Jaune Brillant, Naples Yellow, Quinacridone Magenta, Ultramarine Blue, Warm Pink. SUPER SLOW (45-90 days): Lamp Black, Intense Carbon Black.
ARTIST HANDBOOKS THAT DISCUSS DRYING AND FAT OVER LEAN A.P. Laurie, The Painter’s Methods and Materials, Dover; Gettens and Stout, Painting Materials: a Short Encyclopaedia, Dover; Ralph Mayer, The Artist’s Handbook of Materials and Techniques, Viking; Kurt Wehlte,, The Materials & Techniques of Painting, Van Nostrand; Reed Kay, The Painter’s Guide to Studio Methods and Materials, Prentice-Hall; Mark David Gottsegen, A Manual of Painter’s Materials and Techniques, Watson-Guptill.
UNDERSTANDING THE 3 OIL PAINTING RULES – Windsor Newton site
When using oil paint, a composition is usually built up using different layers of colour. For example, if you are painting a portrait, you may start with an area of background colour, on top of this you may sketch out the proportions of the portrait with another colour, and on top of that you may add further colours for the detail. The way each of these layers of colour interacts with each other is important and will affect how your finished work looks.
If you want to make the most of your painting, there are three tried and tested rules that will serve you well:
Fat Over Lean
Each successive layer needs to be more flexible than the one underneath. This can be done by adding more medium to each successive layer, which makes each new layer more flexible than the previous one and stops the painting from cracking. Think of the rule as ‘Flexible over Non-Flexible.’
Winsor & Newton has a range of mediums to help create this flexibility within layers. One of the most commonly used mediums is Liquin Original and by using it, there is no need to keep on adding oil to your colour.
Thick Over Thin
When painting with heavy colour, it is best to apply thick layers over thin layers, this is because the thin layers dry quicker. For example if you like the impasto style of the Impressionists with their thick bold brush strokes then it is important to remember that these thick layers need to be upper most – thin layers on top of impasto layers are likely to crack.
Slow Drying Over Fast Drying
It is best to use fast drying colours continuously as under layers. If a fast drying layer is applied on top of a slow drying layer then your painting may crack. This is because the fast drying layers will have dried on top of layers that are still in the process of drying out, and as the slow drying layers dry, they will pull and twist those (fast drying) layers above causing them to crack.