The Bearing Edge
Perhaps the best of both worlds is a bowl with a medium flat lip (circa 2.5-3 mm). This style of lip combines the tonal characteristics of the round lip with the projection and sustaining power of the thin lip. Bear in mind that the bearing edge is only one ingredient in the recipe for the voice of a timpano. How the lip interacts with different types of heads, the volume of internal air in the bowl, and the materials and the process of how the bowl is made must also be factored into the equation.
No matter what type of bearing edge (lip) your drum has, it is imperative that the lip is of a consistent width around the circumference of the drum, it is in plane (flat), and is completely smooth. There is a considerable amount of pressure applied to the lip by the tension of the head as it moves across the lip and in order for it to move smoothly without binding or squeaking, some sort of lubrication is usually necessary. Over the years players have used graphite, paraffin, oil soap, curd soap, ox gall soap, ChapStickTM, lanolin and cork grease, and a host of other substances to lubricate the bearing edge, but more recently various products made from the synthetic compound PTFE (polytetrafluoroethylene) have come into vogue. Among them are PTFE tape, PTFE spray and dry PTFE powder.
The PTFE tape (Teflon tape, 3 mil thickness, 5/8″ wide) is probably the most widely used by manufacturers, but the PTFE spray comes highly recommended as well. Both have their advantages and disadvantages. The PTFE tape is relatively expensive and can wear-out over time. The PTFE spray is messy and often difficult to apply evenly to the lip, plus it is detrimental to your health if inhaled. Teflon is inert so no chemical will will completely dissolve it. If it has highly impregnated the lip of the bowl, you will likely have to remove it by mechanical means. There are no commercially available solvents for PTFE and the only way to remove it is by grinding of burning. When using the aerosol PTFE spray, take extreme caution and use in a well-ventilated area only.
The author has used 1 inch Rulon tape (a PTFE derivative) as a lip surface on drums with wide rounded lips with great success. Rulon tape is a few mils thicker than the traditional Teflon tape used by some professional timpanists. Because of the wider lip, the drums are excellent for producing a period sound with slightly less resonance and sustain, yet yield a prominent principal tone.