If you are creating new icons for the toolbar, action bar, stationery, letterhead, or any other part of the client, you must adhere to the following Icon style guidelines (see figure 1):

NOTE: These are general guidelines for a 16x16px icon; larger icons may require larger shadows, inner glow, and edge.

Lighting
Light Source: 120 degrees
Shadow: 120 degrees -- Black 20% black opacity, 0% size, 0 pixel spread
Inner Glow: 1 pixel
Edge: Gradient from top left to bottom right

Size Requirements
Toolbar: 16x16 png
Action bar: 18x18 gif
Tabs: 16x16 png
View Type: 12x10 gif
Status Bar: 12x10 gif
Letterhead: 65x65 gif

States
Hover: The hover effect is done programmatically on the background
Disabled: You need to provide a disabled effect. If you have Adobe Photoshop, then you can run an action. Specifically, put the “create disabled.png_18x18.atn file in your Adobe/Photoshop/Presets/Photoshop Actions folder and select this action when you run a batch on the files that you want to make disabled. It will overwrite the file, so ensure that you save the icons in a separate disabled folder before running the batch.

Figure 1. Summary of Icon style

See also:

Visual style.
Making your Lotus Notes application conform to the Notes 8 visual style.
Visual style for composite applications.