The interior surface of a blowhole which lies near the outer crust of the ingot, as at A in fig.
With the white LED fans the top blowhole looks ace.
To make the bottom blowhole I cut out the hole with my trusty dremel.
A single blowhole is located on a slightly raised lump on the front left side of the rostrum.
I have since installed a side blowhole with a 5v fan blowing in air, which makes a huge difference.