Custom Icon Sets for ExtJS tool types
December 11th, 2014

according to the ExtJS documentation, these predefined types are available:

collapse, expand, maximize, minimize, resize, restore, move, close

minus, plus, prev, next, pin, unpin, search, toggle, refresh

save, print, gear, help

right, left, up, down

one can enter whatever type one wants:

{type: 'YOURTYPE'}

while providing a 15px icon – or preferably icon sprites
(the background-position certainly not applies for single icons, but icon sprites):

.x-tool-img.x-tool-YOURTYPE{
   background: url('../images/custom_tool_sprites.png') no-repeat 0 0;
}

External Links:
Ext.panel.Tool-cfg-type