Uni Liquid Chalk Markers utilise water-based pigment ink so you can mark on windows, glass, mirrors, plastic and metal surfaces with ease. The ink won’t wash off in the rain, yet is easy to remove with a damp cloth. For permanent application the markers can also be used on chalkboards for a bold statement. - Each marker has a broad 15 mm tip for thick lines. - It's suitable for use on windows, glass, plastic, metal and for both indoor and outdoor purposes. - The water-based ink is bright and vibrant.