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Ashley Back in 1999 I used the services of Morelli & Co who were based at 52-60 Baker Street High Wycombe HP11 2RX.
They used their reference library and many Fish slides to establish correct mix for my 1949 Bordeaux Red paint for my 1949 Std VW Beetle.
Despite the many changes in rules and regulations which have occurred over the years regards cellulose v water based paint , Morelli were able to mix the correct colour, they even offered to mix in a dulling agent in order to achieve the correct finish.
If they no longer exist in High Wycombe their Head office was unit2 Baird Road, Enfield, Middlesex, EN1 1SJ ...e-mail at the ime (1999)
headoffice@morelli.co.uk.
Not sure if this helps but you never know till you have tried....[
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Good Luck
Keith