Faithfull FAITLMARKERS Red and Black Tile Marking Pencils Pack (2) are ideal for marking surfaces prior to cutting and shaping. Can be used on ceramic,glass,plastic and metal surfaces. The line drawn can be easily rubbed off after use.The markers’ easy-peel action means that no sharpening is required. These markers can be sharpened with a knife if a fine edge is desired. Always test the marker first on a spare tile as permanent marking may occur on certain natural or unglazed materials i.e. stone and porcelain.