In making the red oil used in French polishing, the alkanet root is merely broken into small pieces and the oil poured over. If well stirred up a reddish tinge will at once be imparted; leaving the root in the oil overnight will yield a stronger red. The red oil is usually kept in a large jar, more oil or root being added as required. The addition of a little turpentine assists in fetching out the colour if the root is very dry.