This technique is possibly for the more experienced and serious mosaic artists. It's used most often when creating a mosaic using a variety of materials that are different thicknesses. It is challenging for a couple of reasons. Firstly, the side of the tile that you eventually want to see, is placed face down and glued onto paper or pushed onto the rolled clay slab. As seen in the diagram below, the thicker pieces will protrude above thinner mosaic pieces. Once all of the pieces have been positioned facedown to create your design, a scratch coat of mortar or a thick resin paste is buttered across the top face, carefully filling any gaps and spaces so there is a reasonably level finish. This becomes the surface for your final back mounting to attach to. When that has dried, you flip over your mosaic, wet down the brown paper and water based glue and carefully pull off the paper to reveal your flat, beautiful mosaic artwork!