Ken Hurst and I are Carolina neighbors and I do some of his assembly,etc. in my shop. We have discussed his method of arriving at french grey several times. If memory serves me it goes like this. 1.Anneal and engrave piece. 2.Color case harden by charcoal pack method. 3.Remove colors using toilet bowl cleaner. 4.Cover surface with the dirtiest diesel crankcase oil you can find. Then Viola', "french grey". Best, Dr. BILL