Abstract: Apparatus and process for marking a surface with a highly visible and substantive mark comprising mixing a dry granular, free-flowing superabsorbent polymer powder with liquid, preferably water, and dye to form a semi-solid gel and depositing the gel onto the surface to be marked. The marking apparatus comprises a chamber for mixing the gel and a ram used to eject the gel from the chamber without excess mechanical agitation and without causing significant breakdown of the gel. The dye makes the gel very visible, the bulk of the gel makes it more easily visible, the nature of the gel makes it temporary; easily dispersed with time, sunlight or water.