Oils present a dense medium that blends color by mixing thick medium
rather than through an overlay function. The Oil Brush 
can
potentially be loaded with multiple colors across the head. Mixing with
oil already on the canvas results in smearing and blending. Shininess
is important, as well as the existence of texture from the mass of medium
on the canvas interacting with the bristles of the brush, as well as the
texture of the canvas.
There are a number of options for managing the reloading of the Oil Brush tool head between strokes:
Reload with solid color
Reload from an area on the Mixer palette's Mixer page
Reloaded with its current contents (dirtied by interaction with the canvas, with optional amounts of mixing in solid-color or color from the Mixer page)
Not loaded at all, but instead relying on the user to dip into the palettes or canvas manually after each stroke.
These options helps to mimic real world paint tools while also allowing the digital user to take a more convenient approach to applying new paint strokes.
Paint strokes applied by the Oil Brush and Palette Knife are, by default, wet in terms of how strokes interact with other strokes by smearing/mixing together. You can, however, choose to dry the Art Media layer at any time. Conversely, you can choose to make a dry Art Media layer wet again:
Choose Layers > Dry Art Media layer (or right click on the Layers palette and choose Dry Art Media layer from the context menu) to dry the strokes applied by the Oil Brush or Palette Knife.
Choose Layers > Wet Art Media layer (or right click on the Layers palette and choose Dry Art Media layer from the context menu) to make dried Oil Brush or Palette Knife strokes wet again.
Note: Both the Dry Art Media layer command and the Wet Art Media layer command can be selectively undone in the History palette.
Oil Brush tool options include:
Shape: Choices include Round or Square.
Size: Defines the size of the tool head in pixels. Note that you can also adjust the Size setting via the keyboard.
Thickness: Defines the aspect ratio of the tool head. Note that this setting is only active when the Fixed angle Head Tracking option is chosen.
Rotation: Defines the angle of head rotation in degrees
Head Tracking: Choose Track path to have the brush head bend around the path of the stroke, or choose Fixed angle to have the brush head remain at a fixed angle.
Head Loading: Defines (in percentage) the amount of material on the brush at the start of the stroke.
Viscosity: Defines the rate at which the material on the brush is applied, and thus the length of the stroke before your paint runs out.
Firmness: Defines the amount of splay in the brush, how the rendered line gets wider with more pressure, and how well it penetrates the surface on to which it is painting.
Bristle size: Defines the bristle size affects the underlying noise function for texture and application of paint.
Reloading: the method by which the brush is reloaded after a stroke. As noted above this could involve requiring the user to "pick up" paint from the canvas or mixer, automatically reloading, cleaning and reloading the brush, or other options.
Auto Clean check box: When marked, this check box simulates cleaning the brush and dipping it in fresh paint at the start of a new stroke. When unchecked, the brush head is not cleaned at the start of the stroke. Instead, the "dirty" head has a small amount of the current color added to whatever dirty head state exists from the previous stroke.
Clean button: Click this button to clean the head and start the next stroke with fresh paint/pigment. Note that this button is only active when the Auto Clean check box is not marked.
Trace check box: When marked, the current Art Media tool will select the pigment/paint color by sampling the data below the center of the brush regardless of the layer type. (This feature works much the same way the Clone Brush's Sample Merged tool option works). When you hold down the mouse button to begin the stroke, note that a single sample is performed, and the resulting color is used for the duration of the stroke.
Note:
The Auto Clean check box and the Clean button are only available with the Oil Brush and Palette Knife tools.
Like other Paint Shop Pro tools, the Oil Brush comes with presets. To use a preset:
In the Tool Options palette, click the Presets button. This displays a list of preset styles.
From the list, choose the desired brush preset.