A solution of strained and pickled Murtlap tentacles, yellow in color. Soothes and heals cuts and other wounds.
References from the canon
Murtlap essence, or essence of Murtlap, was recommended by Hermione for Harry to soak his hand in after detention with Umbridge (OP15). Later in the school year, Harry recommended that Lee Jordan use it after his own detention (OP25), and Lee later recommended it to Fred and George to help with the boils they got testing their Fever Fudge.