Glass mulch lends a decorative finish to containers, water features, path edges and garden borders, and is a useful way to recycle glass at home. Tumbling glass in a rock tumbler removes its sharp edges and provides a range of finishes from a rough, frosted effect that resembles sea glass to highly polished, smooth glass. Glass tumbling progresses in stages and takes up to two weeks to complete, using grit that ranges from coarse to fine. Select thick pieces of glass for turning into mulch because thin pieces break easily, creating sharp, dangerous edges.
Put on thick leather gloves and safety glasses, and place glass pieces on an old towel on a hard surface outdoors. Fold the towel over the glass pieces and hit them with a hammer to break them into a range of sizes 1/4 through 3/4 inch in diameter.
Fill a rock tumbler half full with glass pieces. Add 2 heaped tablespoons of ceramic pellets and 2 ounces of coarse grit per pound of glass, and 1 tablespoon of baking soda. Add water until it just covers the tumbler contents. Close the tumbler and start it.
Turn off the rock tumbler after four or five days and open it. Remove and rinse three or four glass pieces, taking care that the gritty residue does not escape down a drain. Examine the glass for sharp edges. If the sharp edges are worn away, remove and rinse all the pieces and the ceramic pellets thoroughly, and rinse out the tumbler. If the glass pieces are still sharp, rinse the tumbler lid and seal, close the tumbler and run it for another day before checking again. Tumbled glass can be used at this stage if a frosted appearance is the desired effect.
Place the glass pieces in the rock tumbler and add sufficient ceramic pellets to fill the tumbler halfway. Add 2 ounces of medium grit per pound of glass and 1 tablespoon of baking soda. Add sufficient water to just cover the tumbler contents. Close and start the tumbler.
Stop the rock tumbler after two or three days. Remove the glass pieces and ceramic pellets and rinse them thoroughly, and rinse out the tumbler. Place the glass pieces in the tumbler and add sufficient ceramic pellets to fill it halfway. Add 2 ounces of fine grit for every pound of glass and enough water to just cover the tumbler contents. Start the tumbler and leave it to run for three days.
Stop the rock tumbler, remove the glass pieces and pellets and rinse them and the tumbler thoroughly. Place the glass in the tumbler and fill halfway with ceramic pellets. Add 1 ounce of cerium, tin oxide or aluminum oxide per pound of glass, and 1 teaspoon of pure soap detergent powder. Add sufficient water to just cover the tumbler contents, start the tumbler and let it run for four to seven days. Remove and rinse the glass pieces thoroughly. At this final stage the glass pieces are smooth, clear and polished.