This is a demo study of round objects painted indoors in incandescent light. It is more difficult to differentiate the shadow from the light masses in round objects than it is in blocks. We are challenged to find the light and dark masses without the help of the clearly defined edges of the blocks. However, if we keep an image of our block studies in mind when assessing the set-up, we have more chance for success. Imagine a block sitting next to one of the clementines. Ask yourself where will the shadow and light masses fall? Transfer that information to your round objects. Simplify the shapes into one light and one dark mass.
When painting, remember to keep the light and the half-lights in the light plane for the first few passes. In the above study, you can see how the light masses are clearly defined even though there are color changes within the mass. The colors in this light mass all stay within the "light" family. It all reads as light.
The same principle follows for the shadow masses, the value must stay in the "shadow" family. When you are looking at your set-up, squint your eyes until the colors you see in the objects reduce themselves to only light and dark masses or shapes. When you paint the shadow mass, even though there may be several color changes within the shadow, make sure the shadow shape maintains its value integrity. Observe the shadow on the white pitcher above. Although there are several color changes within the shadow, they all stay in the "dark" family. When you squint it down, it should appear as one shadow.
Reflected light is difficult to paint correctly. Although the color differs from the other shadow colors, the value of the reflected light must maintain the integrity of the shadow mass. If it doesn't, it will not read as reflected light, but will appear as an odd shape instead of part of the shadow. In my demo above you can see reflected light from the clementine on the bottom right side of the pitcher. This reflected light does not seem quite dark enough to me. It almost pops out of the shadow family into a lighter value. I've kept it this way so you can see for yourself. Squint it down and observe how it just barely (if at all), stays within the shadow mass.
When setting up a still life for practicing round objects—vases or fruit—make sure you choose objects that have a solid color. Variegated fruit or shiny or transparent vases are not good for seeing the color changes in the masses. Stick with opaque solid colors in your objects and in the cloths. Keep practicing!