James Keller & Sons Dundee marmalade “D”

[Taffoftitchfield]

Hi everyone I’ve got a James Keller marmalade jar that’s been in the potting shed for years . I’m moving so was sorting the shed out and thought oh that looks interesting … which is how I found this forum. It’s really dirty and not sure how best to clean it without harming it - any advice please ? Haven’t seen a reference to a D version in articles

Kel