Definition - What does Free Ash mean?
Free ash is incombustible inorganic matter remaining after fuel burning or mineral mining. The quantity of ash present in a given metal can be examined to determine the rate of corrosion in a material.
Corrosionpedia explains Free Ash
The greater the amount of ash present in a material, the lower the purity of the material with a corresponding higher rate of corrosion, and vice versa.