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If the surface is very rough, it will be tough to create a smooth finishing surface. Of course, one factor that determines the smoothness of the picture is the type of canvas you are using. The trick here is to find the right amount of oil paint you need to use. Similarly, if you are using a very thin layer of paints, the brush strokes will surely be visible, no matter the type of brush you are using.
In this case, it is very likely you will see the underneath color, and the efforts to blend in two colors would leave the surface uneven. It can be tough to blend two layers of paint, especially if they are different colors. These layers need to be thin so that the picture would seem good in the end. When you are painting with oil paint, the most usual technique would be to layer the paints – to paint one layer and let it dry and then to paint another layer on top. This has nothing to do with the properties of oil paint, only with the quality of the paintbrush itself. It is normal for stronger bristles to leave a trace behind them when you are using them. If the bristles are too hard, you will likely see strokes on the paint itself. One of the reasons may lay behind the type of paintbrushes you are using. There are several reasons why your painting may look uneven when you finish it. 1.4 Sources Why Oil Paintings Don’t Have Smooth Finish?.