This is just a short discussion of one of the most difficult aspects of the wet-on-wet painting technique. As anyone who has tried knows, making mountains that way that Bob Ross does is nearly impossible, at least for beginners. The problems can be broken down into two categories: the underlying layer and the highlights.
For the underlying layer, I am referring to the basic shape of the mountain that we block in using the knife and a combination of dark colors (usually blues, browns, blacks, and reds). One of the things that you will notice Bob saying is that after he blocks in the shape of the mountain, he scrapes the canvas with the knife to remove excess paint. After he scrapes, then he uses a brush to pull the paint in the direction he wants and, again, remove excess paint. The theme here is the removal of excess paint and just how much paint you need to remove all depends on the brand of oil paint you are working with.
If you are using the Bob Ross oil paints, you probably already know that the dark colors are drier and thicker than the lighter (whites) colors. What this means is that the darker colors have less oil in them and as we all know from watching Bob, a thin paint sticks to a thick paint in this technique (incidentally, this is the opposite of what occurs in traditional oil painting). If you are not using the Bob Ross oil paints, then you will find that the “wetness” of the colors varies greatly with the brand. The more expensive the paints, the more likely there is to be a difference in oil content between colors. With less expensive paints, the oil content is relatively uniform across the color spectrum.
Using the information about your specific paints, there are two methods that you can use to help improve the look of your mountains and prevent the “mud-mixing” that Bob refers to in The Joy of Painting. The first technique is to scrape away as much of the dark underlying layer as possible. If you are using Bob Ross brand paints, then his technique is probably sufficient. If, however, you are using another brand of paints then you will need to use a little more elbow grease. I have found that the following technique works well.
1. Block in the mountain and scrape it as Bob instructs. Pull the paint with a clean dry brush.
2. Go back and scrape with the knife again.
3. Clean the brush and pull the paint out again.
4. Repeat steps 2 and 3 several times. I find that 3 repeats is a good number, but it all depends on your paints.
What you are looking for is the canvas to show through just a small amount, indicating that you have finally removed enough paint.
Following the above steps helps to ensure that you have only the minimum amount of paint necessary on the canvas. As we have discussed, less is always more in the wet-on-wet technique.
Now the time comes for adding highlights. One of the issues that a lot of people have is the highlights come out looking streaked instead of like areas of more or less snow as in Bob’s paintings. The first way to deal with this is to use the above technique to reduce the amount of underlying layer to the minimum possible. The next way to combat this problem is to change the consistency of your paints. When changing the consistency, you can take one of two routes: Thicken the under layer or thin the highlight paints. Thickening oil paint is difficult unless you are mixing the paints yourself and can control the oil content. The only real solution that I have come across is to let the paint air dry for a day or two before you use. This technique has the advantage that you won’t have to thin the highlight colors as much and then they will be less prone to being picked up as you paint trees, etc. over top of them.
The second route to changing your oil paints is to thin the highlight colors. The best way to do this is to go ahead and mix the colors to create your highlights and then add linseed oil to dilute/thin the paint. Work slowly and add the oil a little bit at a time. This will take some practice to get right. The downfall to this method is that you are likely to pick up a lot of paint as you try to place trees and other objects over these colors. The only solution to this is to further thin the paints you are using to paint the trees, etc. with something like paint thinner or more linseed oil. Be careful about using too much linseed oil as your paints will start to run and mix together. You can see that this method will likely start you down the road of thinning all of your paints as your work progresses.
The answer to the mountain problem lies in practice and in combining the techniques listed above. Remember that less is always more in this technique, so the less paint you use when putting down base layers, the more successful you will be as your work progresses.