The materials are automatically
arranged in ascending alphabetical order, from left to right and
top to bottom:
Click Sort Materials (Z > A)
to reverse the sort order of materials:
You are not obliged to sort materials
alphabetically. You can click one or more materials and drag them
to their new location if you wish to set them in a specific
order. You can do this material by material, or use
multi-selection capabilities (press Shift and
Ctrl).