What are 'blooming' tyres?

Q. I’ve heard some track day veterans commenting on how their tyres have “bloomed”. What are they on about?
Jamie Spencer, email
 
A. “Bloom” is tyre-speak for when an ingredient in the rubber migrates to the surface. You see the same effect on chocolate when it’s been kept for a while with those white-deposits on your Dairy Millk.

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Track day enthusiasts will often have ‘blued’ tyres – where the oil has bloomed and migrated to the surface. It’s not that detrimental, more an aesthetic effect that some people see in the same light as scuffed kneesliders as a sign of a good pace.