These Faithfull Tile Markers are suitable for marking ceramic surfaces prior to cutting and shaping. May also be used on glass, plastic and metal surfaces. The line can be easily rubbed off after use.The markers\' easy-peel action means that no sharpening is required. However, these markers can be sharpened with a knife if a fine edge is required.WARNING: 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.The pack contains one red and one black marker.