How does the fat over lean rule apply?

As per Winsor & Newton:

"Oil painting with Artisan requires attention to the same oil painting rules as conventional oil colour:

Fat over lean (flexible over less flexible). When oil painting in layers, each successive layer must be more flexible than the one underneath. This rule is maintained by adding more medium to each successive layer.
Thick over thin. Thick layers of oil colour are best applied over thin under layers. Thin layers on impasto paintings are likely to crack.
Slow drying over fast. Slow drying colours should not form continuous under layers as any faster drying layers on top may crack. "

I think it would be a good idea to make a list of mediums and continue adding to them and to put them in order of fastest drying to slowest drying medium in order to be able to maintain the Slow drying over fast drying rule. I think it's important to understand in order to avoid problems with cracking.

The ones I think I know are from fastest drying to slowest drying are:

Lukas Berlin Quick Drying Medium
Winsor & Newton Fast Drying Medium
M. Graham Walnut Alkyd Medium
Linseed Oil (All brands I would think)

Where would the following mediums fall:

Water
Winsor & Newton Thinner
M. Graham Walnut Oil
Winsor & Newton Saflower Oil
Winsor & Newton Stand Oil

I just heard back from Winsor and Newton regarding this inquiry:

"If you add thinner to Artisan Quick Dry Medium is this mixture leaner then Artisan Quick Dry on its own.

Is artisan Quick Dry Medium on its own leaner then the paint."

Response:

"Thank you for your inquiry regarding the fat over lean rule.

Basically, fat over lean is just another way of saying "more flexible layers over less flexible layers". A paint layer that has a higher quantity of oil in it remains more flexible and is therefore known as a "fat" layer. A paint layer that has less oil in it remains less flexible and is therefore known as "lean". If
you place a less flexible layer of paint on top of a more flexible layer of paint it can be a little like painting on a rubber band. If you apply paint to a rubber band, allow it to dry, and then pull the rubber band, the paint layer will crack and flake off the rubber band. The same thing will happen to less flexible layers of paint over more flexible layers of paint - as the more flexible layers of paint move while drying, the less flexible layers will try to move with them, but will ultimately be unable to, resulting in cracking. The safest way to keep to the fat over lean rule is to increase the amount of oil (in the form of a drying oil such as linseed, or a medium) added to each subsequent paint layer.

Adding thinner to the Artisan Quick Dry Medium will make it "leaner" than Quick Dry medium on its own, because the additional
thinner will dilute the oil in the medium. Answering your question regarding Quick Dry Medium being leaner than the
actual paint is a bit trickier. Different colors may contain different amounts of oil, due to the nature of the pigments that are contained in the color. Some pigments require a greater amount of oil than others, for even dispersion. Frankly, I really can't give you a definite answer on this one, because I don't know the exact recipe for each color (this is proprietary information and they won't even share it with me!) and each color would have to be looked
at individually.

Janet, I hope this has helped somewhat. Please do not hesitate to contact us again if any of the above is confusing or if you have any further questions.

Amy Faris

Winsor Newton Technical Support"

Updated list:

Winsor & Newton Thinner
Lukas Berlin Quick Drying Medium
Winsor & Newton Fast Drying Medium
M. Graham Walnut Alkyd Medium
Linseed Oil (All brands I would think)
Walnut Oil
Saflower Oil
Stand Oil

Janet wrote:

...Where would the following mediums fall:
Water
Winsor & Newton Thinner
M. Graham Walnut Oil
Winsor & Newton Saflower Oil
Winsor & Newton Stand Oil

Technically water and thinner are not mediums, but dilutents. Water certainly dries fastest, and the thinner would be next in line. Stand oil dries slower than refined linseed. Not sure about walnut oil and safflower, but slower than linseed.

BTW, Holbein also has a stand oil and quick drying medium, and Grumbacher Max has a quick dry. There is also a "painting medium" of a few of these brands that is a linseed oil with drier. Both Holbein and W&N also have impasto pastes that supposedly speed drying times. I haven't tried them all so I can't offer comparisons.

Thank you David for your help! I'll be picking up some the quick drying medium from Holbein to test out.

So this is what we have so far. Some of these I was able to find on the internet:

Water
Winsor & Newton Thinner
Lukas Berlin Quick Drying Medium
Winsor & Newton Fast Drying Medium
M. Graham Walnut Alkyd Medium
Linseed Oil (All brands I would think)
Walnut Oil
Saflower Oil
Stand Oil

I'm no expert but I don't worry too much about it, that would ruin the pleasure of painting. I do start with a thin " liquid white " made up of Titanium White thinned with W/S thinner. After that whatever sticks I put down, if it doesn't stick I thin it with a little thinner and a drop or two of W/S Linseed Oil. If my things ever get to the point they sell I might pay a little more attention to the thick over thin rule. I don't use any other mediums. But I paint for fun, not for the market.