just got my vintage coticule in original box it was an old barbers hone.just under 5inch and just over 1inch wide. It was glued in the box for some reason i have got it out and the other side is bbw. Why is it barbers never used the blue side any one no? and how would they of used the yellow back then i have spoke to a barber that used natural coti i have seen it and he says they used it with water and he spent hours sharpening razors for his dad but when i mentioned slurry he did'nt no what i was talking about. He said he used only water what i carn't get my head round is how would abarber keep arazor realy sharp on a coti with just water