Piranha solution

Piranha cleaning solution, also known as piranha etch, is a warm mixture of sulphuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂), used to clean organic residue off of substrates. Because the mixture is a strong oxidizer, it will remove most organic matter, and it will also hydroxylate most surfaces (add OH groups), making them extremely hydrophilic (water compatible).

Many different mixture ratios are commonly used, and are all called piranha. A typical mixture is 3:1 concentrated sulphuric acid to hydrogen peroxide solution (such as a 30% hydrogen peroxide stock solution). Other protocols may use a 4:1 or even 7:1 mixture. A closely related mixture, sometimes called "base piranha" is a 3:1 mixture of ammonium hydroxide (NH₄OH) with hydrogen peroxide.

Use rubber gloves and a face shield. Perform the reaction in a fume hood or outdoors. To create the piranha bath, one typically starts with a bath of sulphuric acid, to which the peroxide is carefully to be added. One must always add the peroxide to the acid, not the other way around. The mixture reaction is exothermic, hence the solution will become hot. Once the mixture has stabilized, it can be further heated to sustain its reactivity.