Is Alkyd medium, such as Liquin or Galkyd, considered fat or lean?
Introduction:
Is Alkyd medium, such as Liquin or Galkyd, considered fat or lean? I've wondered about this since I began using alkyd mediums in 2013. At first glance, it should be lean and most people on the internet seem to believe so, but some confusing facts about this medium puzzled me. I researched some books, websites, and every forum I could get my eyes on to see other people’s experiences with it. The answer is more complicated than it seems. Determining how “fat” or “lean” one medium is, and how to use it concerning this “ancient” rule is more of an art rather than science. This article will show my thoughts on this matter. Note that this is all empirical.
What exactly is an Alkyd medium and how it’s made:
Alkyd mediums are a type of additive that is used to thin out oil painting colors. They accelerate drying time, enhance transparency, and give a glossy or satin finish to the paint film when dry to the touch. Alkyd mediums are also known as alkyd resins or polyester resins and are synthetic compounds derived from the reaction of polyols (such as glycerol) with fatty acids or oils. The name Alkyd is derived from Alcid, which indicates that the compound is made from the combination of Alcohol and Acid(fatty).
The fat over lean rule:
As we all heard during our oil painting journey, the most important rule is to paint “fat” over “lean”. There are two important aspects to this rule; one is to apply slow-drying over fast-drying, and the second is flexible over rigid. Paints mixed only with solvents (turpentine or mineral spirits) are lean, and the ones mixed with drying oils are fat. If you break this rule, there will be “catastrophic” consequences over time, the paint will crack or even peel off. I never experienced this, but some effects can occur over the decades, so this still scares me. The negative effects of not respecting this rule can theoretically occur because the layer that is applied on top, closer to the surface and oxygen, “dries” fast and becomes solid while the layer underneath is still in the process of curing so it will apply tension to the dried layer above. I quote drying because the correct term for oil curing is “Polymerization”. Oils harden or cure in the presence of Oxygen. Only paints that have a solvent that evaporates dry, for example, Watercolour.
Rant:
So this puzzled me because Alkyds are very quick drying and very flexible, which are characteristics of both “lean” and respectively “fat” mediums. They cure by evaporating the solvent in their composition, typically containing a mineral spirit as a vehicle. This is similar to another polymer resin, Acrylic, which loses its water content after drying instead of mineral spirits.
Now comes another problem, Alkyd mediums are not all made the same, and the manufacturers avoid specifying in the technical data sheet their exact formula. The balance between fat and lean in alkyd formulations plays a crucial role in determining their properties. "Fat" alkyds, characterized by higher oil content, produce glossy finishes and enhance flow and leveling, making them suitable for high-quality coatings. In contrast, "lean" alkyds, which contain less oil, are faster-drying and more durable, making them ideal for environments where quick turnaround and resilience are essential.
Another question I had was: What is leaner? A paint straight from the tube or the same paint mixed with some Alkyd? The straight-from-the-tube paint might dry slower, but it has a lot less medium to it and is less flexible.
The consensus on the forums is that “alkyd” is lean because it’s not an oil, it’s a resin and resins are “lean” like any other polymer that dries with the evaporation of the solvent. But after further research, one would say it is “fat” because it derives from oil and the fabrication process includes adding fatty acids, and it can also leave traces of oil content after the evaporation of solvent.
Brands of Alkyd mediums:
In my artistic journey, I used three brands of alkyd medium:
Liquin by Winsor & Newton, from which I bought all varieties that they produce, Original, Gel, and Fine Detail.
Alkyd Medium by Lefranc & Burgeois. This one is similar to Liquin Original, it has more body to it and can stay stiff on the palette.
Galkid Lite by Gamblin. This one is similar to Liquin Fine Detail, very runny with more solvent content.
From my experience, all of these dry overnight, but I feel like the Liquin original by Winsor & Newton and Alkyd Medium by Lefranc & Burgeois dries a bit faster in comparison to Galkid Lite by Gamblin. The latter has more solvent to it so it’s natural that it will take more time for its solvent to evaporate. The smell of Liquin and Alkyd Medium by Lefranc & Burgeois are very similar which tells me they are made using the same oil, I would guess they are made in the same factory as some art materials from Lefranc & Burgeois and Winsor & Newton have the same source as I saw with their technical data sheet of Sansodor and Odorless Mineral Spirits. Galkind lite has a different smell to it, probably because it’s made using Soy oil.
Conclusion:
I believe that concerning the fat over lean rule, the drying part is more important than the flexibility part. The fact that the drying time of Alkyd is so much quicker than Linseed or Safflower oil is what matters in my opinion. Even if Alkyd can have traces of oils in it, after the solvent evaporates, it’s still in less quantity than pure linseed oil for example. On the other hand, a paint film with a lot of Alkyd medium can be considered fatter than a paint film with very little linseed oil in it, like a paint straight from the tube, because it will be more flexible. So my conclusion is that, in most cases, Alkyd is lean and I will treat it that way in my paintings. This means I won’t glaze over a painting if I use any kind of oil before and will use it only for the first layers of the painting, preferably even in the first one. But then there’s the question: What if I let my painting dry for at least one year, can I ignore the fat over lean rule? Does it all reset because the oil is completely dry? I think so, and this is another factor to take into consideration; How much time do you wait between layers? If you wait long enough, over one year, the fat over lean rule should not matter anymore. However, oil keeps polymerizing for decades at an extremely slow rate after the first year, but this can be ignored in my opinion.
I hope this information will be helpful to you in reaching your own conclusion. Only future generations will be able to see how this medium really behaves in time. If you have some weird experience with this medium, please share it with me in the comments section, I would love to discuss it!