Last year I signed up for an online art course with Scott Christensen (studio in Idaho and retail shop in Wyoming).  I like his work and there are aspects of it that I need to learn.  The course is called "Adventure Of Painting" (or AOP).  There is a charge for it.  His website contains full information about Scott and the course (https://www.christensenstudio.com).  Truth be known, I have not been able to devote sufficient time to it, so after breaks I go back and repeat some lessons.  While not the best way to take the course, it is still very worthwhile, even with limited time.  

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Scott primarily paints using oils.  However, he also produces a large volume of paper sketches using gouache paints.  If you want to know more about different kinds of paint, go for an "AI Overview".  I am still getting familiar with them, so course work is being done with my water soluble oils (WSO).  One example is shown below with the original photo and a many times reworked study. There are still areas in it that need more work.