El Garro using sand to level out the rise and fall of the applied heat is not a new idea though I do wish I could say I thought of it, but I would be a couple of hundred years too late. It works so well because sand is a poor conductor of heat so fluctuations are rendered much slower because of the sands poor heat conductivity.
I would like to pass on the origins of using this method of bluing steel only using heat and no other chemicals.
If you look at a very high quality time piece one of the things you will notice is that the screw heads the clock hands are a striking colour of blue, all produced by using heat alone. Now I am sure that at some time or other you have heated a Steel screw in a flame to turn it blue and that colour is fine, now the clockmakers of times past realised that if you polish the screw heads and clock hands to a high polish finish. Then by heating them up very slowly the oxide layer on the metal thickens and the finer the blue colour becomes, so to keep things stable they used sand as a heat buffer. And that is how the screws and hands on old quality time pieces have that wonderful deep translucent blue colour.
Of interest to some folks and may be not others.
