Several kinds of marks can be applied to ceramic parts. Pre- and post-firing marks can be made. The pre-fire marks withstand high temperature heat treatment and would be useful for identifying tile bodies before glazing or ceramic containers used in high temperature manufacturing processes. The materials used to make these marks are similar to the used for marking glass. Marks can be made both "additive" and "subtractive" fashions.
Post-fire marks on the back of floor tile can be made after spraying a marking formulation onto the surface. This marking formulation sinks into the tile and turns black upon irradiation with the laser as in the picture on this page. This mark would be applied and marked after the tile glaze has been fired onto the top of the tile. Such a mark would allow a manufacturer to apply a glaze to a tile and mark a color and/or customer specific code on the reverse side of the tile. Marking this way eliminates the need for stick-on labels and may serve to help reduce inventory, since the numbering for different customers could be changed on the fly. This material works well with white-colored tile bodies and is environmentally preferred.
Marking on porous ceramic substrates really proves the utility of tapes for marking. The tapes help to prevent marking materials from sinking into the pores of the ceramic surface, serving to increase the contrast by keeping the "white" areas more white.
It is also possible to ablate material from the surface of ceramics, increasing the versatility of the marking process. In this instance, a sprayable marking material is applied to the surface of the tile and ablated using the laser. These marks are also capable of surviving high temperature firing.