This process documents how to create a new .icns file.
Create a Photoshop template file by copying an existing Hog Bay Software Photoshop template. They are stored in resources folder of application target in Xcode directory.
Open template and run /scripts/makeicons.atn. This will generate four images on desktop sizes 128, 48, 32, 16.
Open Icon Composer.app and drag and drop the images into icon composer. Save. And there’s your icon.