Hi, I have just concentrated some H2O2 from a diluted 3% concentration. I used it on a copper scrubbing pad earlier to test how well it would oxidize; but now there is a white, crusty substance where the H2O2 used to be. I then tested it on different surfaces, but every time it dries I get the same white crust. What is this substance? The original solution did not form it. And is there any way to test the percentage of hydrogen peroxide from my solution? Any help would be greatly appreciated!