All of the options you provided are types of shading. Here's a brief description of each:
- Contour - This technique involves creating lines that follow the shape of an object to give it depth and dimension.
- Outline - This typically refers to a solid line that defines the outer edges of an object, but it is not a form of shading in the traditional sense.
- Cross-hatching - This method uses intersecting sets of parallel lines to create varying degrees of darkness or tone.
- Tone - This refers to the use of varying shades of gray (or colors) to depict light and shadow.
Among the options, cross-hatching is most commonly associated specifically with shading techniques.