Woodbine is 100% correct use
Astonish, it's a clay type substance that
comes in a small tub, not very common.
You apply with a damp cloth, works brilliantly.
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"Recommended And Supplied With Aga/Rayburn Cookers"
and they're the expenisve machines
It may be recommended by AGA, but Astonish is actually very cheap and can often be found in the €2 shops. A tub lasts for ages.