text: For display perposes the liquid is just water with a dye. Perhaps if food colouring fades (these are also just dyes) you could try a haberdashery shop that sells fabric dyes which may be longer lasting. \nIt may have been luck that the red dye lasted. \nTo clean the glass we use detergent. Bacteria is removed with a solution of sodium metabisulphite which is available from wine making shops this is then washed out with distilled water and then dried by adding a little acetone, swirling it around and emptying it. The bottle is left in a warm place for the acetone to evaporate. (No naked flames as acetone is flammable)