To make this simplest, what I like to think of is this fat over lean or thick over thin concept with oil painting, where the first layer of paint I put on is my thinnest. So how do I thin down that paint? Well, there's two things to consider. One is adding a fast dry medium, such as a walnut alkyd medium, if you're going solvent-free, or you could use a gal kit or other fast dry medium. Just add more, no more than 25%, 20% to the paint. To load the brush with that thinnest layer, you're going to push a wiggle and really work that color into the bristles. Holding the paint brush parallels to the canvas. You start to work it into the canvas. So this paint will maybe a little translucent in the end. You might have to go back in later and reestablish some of those darks, but this will allow you to get that first layer down nice and thin, which makes it easier to layer on top. This is our lean layer or a thin layer. If you want to be solvent-free, you can get rid of the mineral spirits and to clean your brush, dip your brush into walnut oil. Take it back out, use a paper towel. I like a rag or blue shop towels. And really just wipe your brush into that blue towel, trying to get as much paint off as possible, dip back in the walnut oil and do this until the brush looks fairly clean. That walnut oil can be used again and again. You do not have to dump it out. It may get quite dark over time, but it will be okay. For my second layer of paint, I'm going to take off all fast dry medium from my palette. I'm just going to clean it all off using a paper towel and a palette knife. This layer will be paint only. Again, I can push and wiggle my brush in the paint, but I also might run it over just the edge of the paint. So I have a little bit thicker paint on the brush itself as well. I can paint right over top of that thin layer if this paint layer is a little fatter or a little thicker. Top layers get even thicker. This is where I don't use any medium, but I also don't have to push and wiggle it as much in the brush. I can scoop it out more. And this time, now I might be working a little more parallel to the canvas. So the brush will actually be held at the same angle as the canvas or board that I'm using. And I just have to lay it down gently and then let it be. I can always soften the edges or blur the edges a little bit after I put in that layer paint. To apply that top thickest layer, you can use your brush, but you could also use a palette knife to make really nice thick layers. Usually, this will be your lightest layer as well. Most artists will start oil painting with their darkest values first, which are also your thinnest values, building up your values until your very last layer of thick paint is your whites. That doesn't mean you can't go back and forth and reestablish areas as needed, but it's just a good rule of thumb to work by. Now if I go in and I realize that there's an area I forgot to leave white or whatever the tone to surfaces, and I need to wipe it out or layer on top and I'm having trouble with it, I can take a paper towel and wrap it around my finger or my brush or a tool of any kind and just wipe out the wet area that needs to be the new color. Then I can just paint right on top of it and I don't drag as much of the bottom layer into the paint, allowing for a brighter, more vibrant color. If I just paint right on top of the wet paint, some of the paint from below will mix in. I can also use my brushed wipe out an area of paint. This is the fattest or the thickest paint. Now detail work itself isn't going to be physically fatter because I needed to flow. I need the paint to be less viscous or more runny. So sometimes I can add a little bit of oil medium like walnut oil or linseed oil to the paint and that will help the paint flow a little bit more smoothly so that I can put another layer on top of that very thick layer. Check out my demo Intro to Oil Painting, a light host shows you how you can do this detail work with a brush or a palette knife on top of wet paint.