Spalted wood is wood that has been left outside in the elements until it gets colonised by fungi.  This fungi puts out tendrils or roots thoughout  the wood and where the roots meet another fungi's tendrils they have a chemical fight which results in black lines being deposited in the wood.  Different woods take differing amounts of time to spalt.  If they are left too long they eventaually rot.  The trick is to catch the wood when it has the optimum amount of marking but before it gets too rotten to be viable to turn. 

Ash is an exception to the rule that spalting results in black lines. In this wood, if left long enough, the spalting results in yellow markings not unlike Leopard spots, or the markings on a Giraffe.  Please see the Jigsaw section for a good example of this on the ornamental Giraffe

 

 

This is a spalted ash log ready to be turned.

 

 

 

 

 

 

Ash log on lathe that has been turned round ready to be made into an eccentric candle holder.  The yellow spalt markings can be clearly seen on this log

 

 

 

 

 

This is an example of an ecccentrically turned "T" lite holder.  It is turned from Ash that had been left outside for a while to start spalting.   This is indicated by the slight yellowing of the wood between the grain markings.