Solution 1 was a mixture of sulfuric acid (H The 4 th 2 SO 4 ): orthophosphoric acid (H ): water (10:4:1, v/v/v). Solution 2 was mixture of sulfuric acid: water (2:7, v/v). The specimen was placed into 2 mL of 1% (w/v) of potassium permanganate in solution 1 and shaken for 2 h at room temperature.