some argue that different metals make less difference in sound quality than different flautists playing the same flute. Even Verne Q. Powell, a flute-maker, admitted (in Needed: A Gold Flute or a Gold Lip?) that "As far as tone is concerned, I contend that 90 percent of it is the man behind the flute". Most metal flutes are made of alloys that contain significant amounts of copper or silver. These alloys are biostatic because of the oligodynamic effect and thus suppress growth of unpleasant molds, fungi, and bacteria. Good quality flutes are designed to prevent or reduce galvanic corrosion between the tube and key mechanism. Pad materials Tone holes are stopped by pads constructed of fish skin (gold-beater's skin) over felt or silicone rubber on some very low-cost or "ruggedized" flutes. Accurate shimming of pads on professional flutes to ensure pad sealing is very demanding of technician time. In the traditional method, pads are seated on paper shims sealed with shellac. A recent development is "precision" pads fitted by a factory-trained technician. Student flutes are more likely to have pads bedded in thicker materials like wax or hot-melt glue. Larger-sized closed-hole pads are also held in with screws and washers. Synthetic pads appear more water-resistant but may be susceptible to mechanical failure (cracking). Keywork The keys can be made of the same or different metals as the tubing, nickel silver keys with silver tubing, for example. Flute key axles (or "steels") are typically made of drill rod or stainless steel. These mechanisms need periodic disassembly, cleaning, and relubrication, typically performed by a trained technician, for optimal performance. James Phelan, a flute maker and engineer, recommends single-weight motor oil (SAE 20 or 30) as a key lubricant demonstrating superior performance and reduced wear, in preference to commercial key oils). The keywork is constructed by lost-wax castings and machining, with mounting posts and ribs silver-soldered to the tube. On the best flutes, the castings are forged to increase their strength. Most keys have needle springs made of phosphor bronze, stainless steel, beryllium copper, or a gold alloy. The B thumb keys typically have flat springs. Phosphor bronze is by far the most common material for needle springs because it is relatively inexpensive, makes a good spring, and is resistant to corrosion. Unfortunately, it is prone to metal fatigue. Stainless steel also makes a good spring and is resistant to corrosion. Gold springs