I got a question for those of a scientific mindset out there. I use a mixture of coal dust and water to age my blades. I mix water and dust into a thick, sloppy pudding and then burry the knife in it overnight. Now here's my question: what is the chemical reaction between the water and the coal that creates a corrosive agent? It works beautifully, pitting the blade, and darkening the steel. In fact I've accidently left a project in there for two days, and when I remembered it, there were tiny holes corroded right through the steel. Does anyone know what the chemistry behind this is? Just curious.
"Return unto me, and I will return unto you," saith the Lord of hosts. ~Malachi 3:7b
Posts: 297 | Location: MI | Registered: 18 August 2012
I think it might depend in part on the type...anthracite, bituminous etc. which would determine the specific chemistry. There is some sulfur content in all coal and it sort of sounds like what you are seeing is an evolution into mild sulfuric acid and that might be what is giving you the effect want: etching your blades.
Sua Sponte
Posts: 460 | Location: SW Virginia (New River Valley) | Registered: 13 August 2014
Agreed, I think it's the sulfur in the coal that's doing the trick. Coal is hardened peat, and peat bog are one of the most acidic environments around, so acidic that corpses from 2400 years ago were found mummified (well they were really tanned). Check out Tollund Man.
LD
It's not what you know, it's what you can prove
Posts: 3843 | Location: People's Republic of Maryland | Registered: 10 November 2004
Josh, you can probably change the dilute factor of your acid bath by varying the density of the crushed coal. The finer the crush and the soupier the stew, and if you change the environment it sits in while you're waiting for it to be done, (seal the container, cook it, etc) I think you will find some changes in how dilute/strong the mix is. That can vary the kinds of patterns you can get in your etching. Sounds like a fun project.
Sua Sponte
Posts: 460 | Location: SW Virginia (New River Valley) | Registered: 13 August 2014