Potassium permanganate-sulfuric acid solutions are an etching solution used in metallography to visualize the microstructure of metals, especially stainless steel. The solution consists of a combination of potassium permanganate, a strong oxidizing agent, and sulfuric acid, a strong acid.

Gordon & Sweet etching solution is particularly used to examine stainless steel to visualize grain and phase structures. The mixture of potassium permanganate and sulfuric acid allows material to be selectively removed from the surface of the metal sample, making the various phases and grain structures visible under the microscope. The contrasts produced in the microstructure of the material allow detailed analysis of the properties of stainless steel, such as strength, hardness and corrosion resistance.

Because both potassium permanganate and sulfuric acid are hazardous chemicals, it is important to take appropriate safety precautions when handling the potassium permanganate-sulfuric acid solutions.