Sun Thickened Walnut Oil - My Favorite Medium
My absolute favorite medium for oil painting is Sun Thickened Walnut Oil from Natural Pigments.
Why it's my favorite...
I like this medium because it doesn't thin out my paint and make a slippery mess of the painting surface like regular walnut or linseed oil does. I like the paint in the consistency it is when it comes straight from the tube. Furthermore, this medium does not alter the drying time significantly or cause excessive yellowing. Natural Pigments also makes a linseed oil version of this oil but I prefer the walnut as it gives me more time to work the paint before it tacks up.
How to use the Sun Thickened Walnut Oil
First, it is really important to adhere to the fat over lean rule and also use the medium sparingly. I mean really sparingly. (Unless you are painting enormous paintings one bottle should last for years.) In my first layer I never add any oil to my paint. After I have completed the first pass of the painting, there are some areas which require a second layer of paint to achieve the desired finish. Before I begin the second pass, I place a couple of drops of the oil into the pretty blue dish and dab the makeup sponge lightly into the oil. Then, using the sponge, I apply the oil to only the section in which I will be working for the day. You want a nice even and very thin coat of oil that brings all the colors and any sinking in back to life. Next, I remove all the excess oil from that section of the painting with a clean sponge and commence painting.
It is important that your painting be fully dry to the touch and to apply the oil only to where you will be working that day. If you do not paint over the oil during that session you will have a section of the painting that is covered with a layer of 100% oil and that is trouble!
I add the oil to the second layer of the painting in this manner instead of mixing it into the paint on my palette to ensure that the layer of paint will receive an even quantity of oil throughout, facilitating a more even sheen across the painting's surface. Also, this method enables me to add less oil to the paint than I would if I were mixing it into each individual color. The less oil you add, the lower the likelihood an issue with the layer will develop and the less yellowing your painting will experience as it ages.
Glazing: This medium, due to its consistency, is not ideal for glazing applications. For that I add in a drop or two of Natural Pigments regular walnut oil to the sun thickened version until I have a consistency that I like for glazing.
Studio Tip: At the rate of using a few drops every couple of days, I estimate that it will take me several years to go through one bottle. By that time the excess air in the bottle will cause the oil to polymerize fully and be unusable. To minimize the quantity of air in the jar I add clean marbles to displace the air so this process will occur more slowly.