This is true because the abrasive particles have a greater elasticity than the surface of the bronze, causing them to crumple and absorb the blow instead of the bronze being the one to give under the force. They also found that using walnut shells did not increase the rate of corrosion. Their conclusion was that walnut shells were the superior choice of air abrasive, because it had all of the same benefits as glass beads, but none of the negative side effects. According to David A. Scott, Veloz, Ruff, and Chase’s findings were also confirmed by “Barbour and Lie” who did a series of tests including glass beads, 3 different types of plastic beads, sodium bicarbonate in a powder form, and walnut shells. According to Naudé and Wharton, “Coating materials are selected for their durability, adhesion, ease of maintenance, and surface appearance. The selection of an appropriate coating system is governed by the bronze surface, environmental considerations, and expected degree of maintenance.”  "Clear Trewax Brand Paste Wax"  Trewax brand paste wax is made of carnauba wax (the only other natural wax aside from beeswax) suspended in turpentine  Trewax works well on both light and dark patinas, and is fast drying. However, if used on a warm surface it can smear or cause bulky build up (“mud pack”)  "Johnson Paste Wax"  With Johnson brand paste wax there is a chance that it could cause a darkening of a lighter patina and should therefore be only used on darker patinas if that darkening is not desired. "Renaissance Wax"  Renaissance wax is a hard wax that produces a high shine when it is buffed. It is not always the easiest brand to find. "Kiwi Neutral Shoe Polish"  Kiwi Neutral Shoe Polish can create a “high gloss” if desired and can be used in conjunction with Trewax brand paste wax. It may darken light patinas, and so should only be used with medium to dark toned patinas. "Butcher’s Wax"  Butcher’s wax is composed of paraffin and carnauba waxes as its main components. "Liberon Special Effects Waxes"  Liberon has pre-toned waxes for when more than clear wax is necessary. "Incralac"  Incralac was developed by the International Copper Research Association.