Creating a Cracked Photoshop Brush
We now need to add a new layer to the document, on this layer we will add the main cracked effect. Select the 'Polygonal Lasso' tool 
from the tools menu, now click and draw a jagged shape.
Select black from the swatches tab or press 'd' this will give the foreground the default fill colour which is black. Then (at the top) go to 'edit' then 'fill'. You should now have a jagged black shape similar to the one below.
note The shape above the screw head doesn't really matter as we will be moving it below the head, so it wont be seen.
Now we have to move the new cracked layer, below the screw head layer.
Click on the 'cracked layer' (layer 2) hold down the mouse button and drag it below, so its in between the screw layer and the background as shown in the image on the left. It now should look something similar to the image shown below.
Now we have the basic brush designed we can now Create a brush from it.
