The willow is pressed a number of times, which essentially congeals the fibres running through the timber, making it tougher. Press-ing also affects the final weight
of the bat.
Pressing also affects the feel of the bat. The less the willow is pressed, the lighter the pick-up will feel, even if the weight is the same as a bat that is pressed more.
It is often assumed that today's thick-edged bats are heavier than their traditional counterparts, but this isn't always the case. While players in Don Bradman's era often used bats weighing no more than two pounds two ounces, bats of more than three pounds have been a common feature of test cricket since the 1970s.
According to Cricinfo's Paul Edwards, modern bats are no heavier than this, with the average being around two pounds nine ounces. What's changed is the pressing techniques and design. The thick edges serve to mask the fact that a lot of wood is now hollowed out from the bat either side of the spine.
The basic rules of cricket bat design are fairly simple: they must be no wider than 10.8cm, no longer than 96.5cm, and be made entirely of wood. These prescriptions developed in response to some intriguing innovations.
The first came from a chap named Shock White, who in 1771 came out to the crease with a bat as wide as the three stumps.
In the late 1970s, Australia's Dennis Lillee faced up to the English with a bat made entirely of aluminium, and just a few years ago, Ricky Ponting used a short-lived Kookaburra that was reinforced with carbon-fibre polymer.
There has also been a lot of legal tinkering with the shape of bats to optimise their performance.
Two physical properties are crucial to cricket bats. Firstly, there's the 'fundamental vibration node', which is the point on the bat (elusive to most club cricketers) where the collision with the ball results in almost no vibration. This is commonly called the bat's sweet spot.
Then there's the 'centre of percussion'. When the ball strikes the very bottom of the bat, the handle jars forward. When the ball hits the very top of the bat, the handle jars back. If the ball hits the sweet spot, the handle doesn't jar at all, which increases shot precision.
Bat makers have come up with a number of innovations over the years to maximise the sweet spot. Our own Lance Cairns hit his famous six sixes at the MCG with his shoulder-less Excalibur. Scores of batsmen have plied their trade with the Gray Nicholls Scoop, which distributes weight around the perimeter of the blade in much the same way as game-improvement golf clubs do nowadays.
There's also been the Gunn & Moore Diamond and the Kookaburra Ridgeback to name just two others. The shape of McCullum's bat is just the latest innovation in a fine and quirky tradition.
But perhaps the most radical development of late is the Mongoose, made popular to Kiwi fans by Lou Vincent. The Mongoose looks something like a small rowing oar, with a longer than usual handle and a shorter than usual blade. The idea is that the weak points of the bat are eliminated, leaving only one big sweet spot.
It remains to be seen whether it will catch on.
