The subtlety of the facing is often underestimated: common wisdom has it that the playability is governed by the facing and sonority by the chamber form. This is largely inadequate. The way in which the facing curves has a great influence on the sound produced.
As a starting point for a design serve the curves that reeds produce. On the basis of those curves I construct a facing. This allows for variations in an expected use, a reed, a dynamic range.. Studies have been done in 'thematic' series of mouthpieces in facing design, combining a certain tip opening with a length or a tip angle. This enables a comparison between different aspects of facing design in practice. Facings can now be designed to a customer's request. All facings are checked for symmetry and for being consistent with the proposed plan.
Facing characteristics govern sound production. It helps to define the ease in producing partials or the extend to which wind-to-the-tone can be heard. At the tip, the opening and closing of the reed depends on details of the curve of the facing. Tiny differences play a considerable role. At the lower end of the facing, facing shape influences what is sometimes referred to as 'mass'. Quite well known are the reed adjustment charts for response and tone. Just as it turned out with the reed tip, the facing is the mirror opposite of the reed strength. With the same good reason similar charts could be drawn up for facing heights. In combination with a certain reed a certain lower end curvature proves to be of the essence. Finally, clarity and detail in sound production is defined by the width of the tip rail. Per mouthpiece it is dimensioned to taste and so guarantees a clarity notwithstanding an 'old fashioned' wide and round chamber.
I give a specification of a facing in three figures, adding tip angle: