Burning hammers is a technical term: using a flame (or other warming) to alter the angle of each hammer on its shank.
Burning is done after Travelling. Travelling can only be done when hammer centres are working properly (more on hammer centres anon).
The hammer first in from the left (under my finger tips) looks like it needs burning, because it is not vertical on the hammer shank –
This is confirmed by lifting the hammer, comparing its position relative to its neighbours – ie at rest (pic above), hammer nose was nearer to the left; at lift (pic below), hammer tail is nearer to the right:
After burning, the hammer nose is now closer to the right:
Lifted, this is confirmed – the tail is similarly closer to the right (ie it is now positioned vertically on the hammer shank):
Done burnin them hammers! (well, that one, at least).