Originally from The Nightwatchman, the Wisden Cricket Quarterly, here Alison Mitchell explores the science behind pink cricket balls.
The strong smell of chemicals is overwhelming. Pale blue lambskins are piled high on a wooden clothes-horse, dripping wet. Six or seven cavernous dye drums are rumbling and vibrating, making me want to cover my ears.
These are potent memories from my childhood when I was occasionally allowed inside the leather tannery at Strong & Fisher Ltd in Rushden, where my dad was sales and marketing director. Strong & Fisher produced clothing leather, but at Joseph Clayton & Sons tannery in Chesterfield a significant proportion of the production is cricket-ball leather. Claytons are the UK’s major producer of leather for cricket balls and have been supplying Dukes and Readers for over 20 years. Dukes manufacture the balls used for men’s Test and first-class cricket in the UK.
My mission is to better understand the differences between red, white and pink cricket-ball leather. While many things contribute to the way a ball behaves in a match, a major factor underpinning it is how the leather for that ball is tanned and finished.
Production of leather for a traditional cherry-red Dukes with a hand-stitched seam starts with a raw cowhide. Once the hides have been cured to prevent bacterial breakdown, the hair and flesh is removed, and the skins are pickled, ready for tanning.
During tanning, a chemical reaction takes place between the skin protein and a tannin agent, preventing any further bacterial action.
Alum tanning, dating back 1,000 years, is the preferred method for tanning cricket-ball leather because the chemical bonds produce a strong leather with good durability. Alum tanning produces skins that are easier to dye, and the whitish base colour makes them ideal for producing white and pink leather as well as red.
When the tanning process has been completed in large drums, the skins are thrown across wooden clothes-horses overnight for the chemical reaction to complete and for excess moisture to drain off. Then they are hung or pinned to dry slowly, ready for further processing, which begins with the skins being shaved on the flesh side to a uniform thickness of 3mm.
The skins are now ready to go back into more drums for re-tanning, fat-liquoring (lubricating the fibres in the skin to ensure the leather is supple) and, crucially, dyeing. With the red ball, dyeing gives the leather a pale red hue and variations from one dye bath to the next help to explain slight differences in shade from one batch of cricket balls to another.
Once the leather arrives with Dukes it needs to be “finished”. The finish is critical in explaining the properties of different coloured balls. Leather for red cricket balls is aniline-finished. Transparent dyes, mixed with water, are applied – and there is no artificial covering of the natural grain surface of the skin. The addition of synthetic buck fat (warm liquid wax) gives the leather its dark cherry-red appearance as well as a degree of water repellency as it absorbs into the naked surface. Wax is significant because a fine shellac coating is later applied to the ball, and when this wears off during use, the waxy surface is revealed. With heat generated through friction, polishing of the grain surface can commence. The aniline finish is not colourfast, hence the red marks on cricket whites.
The ability to polish a ball is of vital importance to its performance and behaviour. To date, no tannery or cricket-ball manufacturer has been able to produce a white or pink ball that polishes up in exactly the same way as the equivalent red, although Australian company Kookaburra say they are very close with the pink ball they have developed for the upcoming day–night Test.
White and pink leather for cricket balls has usually been pigment-finished, whereby the desired pigment is mixed with resin and several coats of colour are sprayed onto the surface of the leather. Brightpink leather can be achieved in a dye drum, but if buck fat is applied as it is in Dukes’ manufacturing method, the leather darkens and the brightness of the pink is lost. With a pigment finish, the lighter the colour, the smaller the pigment molecule and a greater number of coats need to be applied in order to achieve a solid, uniform covering of either pink or white.
These spray coats completely cover the grain surface of the leather. Like the red dye, the resin pigment isn’t colourfast but whereas with the cherry-red the dye has gone through the skin, any wearing of colour from a white or pink pigment-finished skin will result in the pale whitish colour of the alum base tan being revealed underneath. In cricketing terms, this is a ball losing its colour. To prevent this, several coats of hard polyeurathene or cellulose lacquer are applied.
The use of a different white ball at each end of a 50-over ODI has helped balls keep their colour, but the effect of the lacquer is that when a player tries to shine the ball, it can be like trying to polish plastic. The natural grain surface of the leather has been completely covered by lacquer and pigment, and there is no heat reacting with buck fat to create shine, as is achievable with the red Dukes.
The ball to be used in the Test has been extensively tested by MCC, and Kookaburra say it is the closest in properties yet to their own red ball, which relies on natural oils to achieve shine rather than the addition of buck fat, and which is coated in a hard nitro-cellulose lacquer. In terms of behaviour, the red Kookaburra is known to swing for a shorter period of time than the red Dukes.
In an interview with the Sydney Morning Herald, Kookaburra’s group managing director Brett Elliot explained that the pink ball is finished in a way that is somewhere between the red and white Kookaburra ball.
“They have identical centres, so in terms of hardness and bounce all three are identical. They also all use the very best of Australian hide which is alum tanned. However, the red and pink leather is dyed, whereas the white is not.”
Elsewhere he says: “The main difference between the pink and red [Kookaburra] ball is that we add a very fine film of extra colour, paint, to the surface of the [pink] ball, and then we put the clear cellulose lacquer finish on both the red and the pink ball.”
Elliott confirmed that after tanning by Packer Leather in Queensland, the leather is drum-dyed by Kookaburra to a pastel-pink colour, with the dye penetrating right through the skin. The film of bright-pink colour sprayed on top is mysteriously referred to as the G7 finish. Elliott would not reveal details of the make-up of this spray coat, but explained that its purpose was to enhance the visibility of the ball. Finally, to preserve the colour, the top coat of nitro-cellulose lacquer is applied.
Pigment completely covers the surface of the leather, forming a barrier to the natural grain. Elliott acknowledges that the pink ball will be harder to polish than the red Kookaburra once the outer layer wears down. “With the red, the top coat does scuff off within the first 10 to 15 overs and then the natural fats of the ball are what encourage the later shining. This feature is still possible with the pink ball, however it is harder to shine. This will mean that teams will need to work hard at preserving the condition of the ball. I suspect this will be one of the challenges.”
Thanks to John Riches (DLC National Leathersellers College) Joe Dewhurst (former Technical Director Joseph Clayton & Sons) and the Society of Leather Technologists and Chemists.