Making tiles from recycled glass
To make glass from recycled glass sources, the raw materials must be free of contaminants (paper, dirt, wrappers, etc.) and must be ofuniform source and color. Typical sources of glass for recycling are bottles, jars or window glass.
Different types of glass have different composition and color; waste glass should be carefully sorted before use. Different glass sources have different coefficients of expansion. As a result, the glass will not cool as a uniform mass. The negative results during cooling can range from cracking to explosion.
Different manufacturing techniques give rise to different results. There are three common methods of making tiles from recycled glass:
Small mosaic tiles are usually made from glass that is brought to a molten state along with glass color, poured over an iron table andpressed with a form (cookie cutter) to create the small mosaics. This technique involves small batch sizes and labor-intensive process of tile sheet assembly.
The glass and color mixture is heated to a high temperature until it achieves a molten state. Once cooled, the pieces are separated and the tiles can be assembled into sheets that are easy to install. This technique is well understood and is relatively easy to set up. The final product consists of small mosaic tiles with some color variation. This variation is not critical, and may even be desirable. One ecological advantage of this technique is that the broken tiles and production waste are kept to a minimum because of the small module of the tile. However, one disadvantage is the high heat required to heat the tile - approximately 1400 degrees C.
Large glass tiles (50mm x 50mm and larger) can be manufactured using the same technique as above, with one added step. The glass must be annealed in an annealing oven (kept at 500 C over several hours) to remove the stress created during the cooling process. Larger tile modules create more production waste, and require more color control and quality control.
Glass tiles can also be made from cullet (glass that has been crushed and sorted into uniform particles) and placed in ceramic molds. This technique involves heating the glass to relatively low temperatures (800 C) followed by annealing. The advantages include lower firing temperatures and a faster production cycle. The disadvantages are - the colors are dictatedby the color of glass cullet available from the recycling stream, i.e. green, brown or clear bottle glass.