Water-based preparation comprises at least one dye comprising triphenylmethane dyes, azo dyes, cyanine dyes and/or natural dyes, where the preparation has a density of 1.01-1.5 g/cm 3>. An independent claim is included for a kit comprising a syringe with cylinder and cannula, and a water-based preparation, where the ratio of cylinder diameter to the cannula diameter is 10-2 to 1-0.2, preferably 20 to 1-4 to 1.
