An alternative theory about the mysterious origins of the white powder on the Ranfurly Shield has been proposed.

The iconic log o' wood was split in two after the Hawke's Bay Magpies dropped the Shield at an after-party celebrating Saturday's win.

Ranfurly Shield restorer James Dwan says the white powder seen in photos is likely plaster from earlier repairs of the famous taonga.

"I put some plaster into the centre part of the shield a couple of years ago to try and reinforce it, because it's a pretty weak area in the metal work itself. I've got a funny feeling that's what's happened.

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