You are probably remembering Alan Crossfield's 1 1/16" scale seven-plank coal wagon.
It was first exhibited at the 63rd International Model Engineer & Modelling Exhibition held at Olympia in December 1993 / January 1994 when it was awarded a Silver Medal. A picture and brief description appear in ME No. 3964 of the 4th March 1994.
It was again exhibited at the 64th International Model Engineer & Modelling Exhibition held at Olympia in December 1994 / January 1995 . A picture and brief description appear in ME No. 3988 of the 3rd. March 1995.
Alan's wagon was however, painted, and you may also be remembering another picture of a 7 plank wagon that appeared in ME 3991 of 21st April 1995 in a report on model engineering societies in North Wales. That was under construction and unpainted.