It is a piece of piss.
You know that stuff you can buy from the supermarket to spray onto carpet stains?
It turns white and powdery and sits on your carpet - when you vacuum it away, your carpet stains have been removed.
Well...you can spray it onto your willow - leave it over night, then wipe/dust it off and WHALLA - your willow looks whiter than ever and sensational.
WARNING: Cover your bat stickers with masking tape as it can bleach them too!
Also, never spray directly onto the splice as it may loosen glue.
I do it all the time and my older bats are rejuvenated.