selenic acid is made by oxidation of selenium dioxide with hydrogen peroxide. it is hard to evaporate it, but when it is evaporated, it makes colorless crystals. it can be made by oxidation of selenous acid with a strong oxidizing agent, such as potassium permanganate, chlorine, or bromine. the hcl and hbr made as a byproduct can reduce the selenic acic to selenous acid again, though, so it has to be taken out.