Thread on edges in painting! Hierarchies of value and color in our paintings are so important and a hierarchy of edges adds a whole other dimension. Edges are particularly fun because we can use a mental checklist to sort out which should be hard, soft, and everything in between: 
1. Where very similar values meet, it feels like a soft edge, and this can be accentuated to what is known as a “lost edge.” Edges are strongly related to value! Notice in this Sargent how the dark values get lost into the shadow entirely and how the arm gets lost into the torso.
2. Where very different values meet, the edge feels harder. For example, a dark tree against a bright noon sky will have hard edges. Look how hard the edge of the light here is against the background (and notice the lost edges from close values too!)
3. Edges are softer in the shadow, and harder in the light. Notice how the edges in the shadow from his hat are softer than the light side. Often the specular highlight, such as on the hat and nose, will be one of the hardest edges, depending on the focus of the painting.
4. Scenes with lower light levels will have softer edges in general.
5. Form shadows (when the form rolls away from the light) are soft, and the slower the plane turns, the softer the edge. For example, the form shadow getting tighter at the wrist to describe the box like shape, and softening up towards the deltoid to describe its roundness.
6. Cast shadows (when light is blocked by an object) from a small light source are hard, and gradually get softer as the distance from the shadow caster increases.
7. Softer edges tend to give an overall effect of motion rather than a moment frozen in time. Notice how the soft edges in this portrait give it a sense of life, and how the Sargent sketch feels like it has more movement than the finished version.
8. Edges can be used to show material differences. Hair, fur, and delicate cloth will have softer edges compared to metal, for example. Notice how in these Sargent paintings the hair and fabric have softer edges than the skin.
This is non exhaustive! Edges can also simulate lens effects such as depth of field. These can all be used creatively and rules can be broken for the composition and that is most important. Having said that, take advantage of simple effective principles where you can find them!
Again, edges are part of a hierarchy and a soft edge from one painting could read as a hard edge in another. Keep your hardest and softest edges in the context of the painting in mind, think of a scale from 1-10 just like you would with value. Everything is relative, so compare!
Artist credit: Walter Ernest Webster, John Singer Sargent, Abbott Handerson Thayer, Isaac Levitan, Umberto Coromaldi, Vlaho Bukovac
Here are links to my previous threads if you are interested!
Composition:
Values:
Exposure:
Highlights:
Composition:
Values:
Exposure:
Highlights:
