Each time we grind a different colour we rinse out the mill and save the pigment residue. Over the year this residue accumulates into a beautiful sludge made up of layers of different colours. When enough has accumulated to make a batch we put it through the mill again and blend it all together to make Vancouver Grey. If you looked at this grey through a microscope you would see all kinds of brightly coloured pigment particles.
Each dated annual batch is a different grey, varying from warm to cool depending on the range of colours mixed throughout the year. Vancouver grey can be a very useful colour for subtly desaturating your mixes. Used in a composition, it shows off the surrounding colours, and is a beautiful colour in its own right.