There is a number of faults that you will meet every now and then in mouthpiece facings. 'Faults', in this context, does not necessarily mean that the mouthpiece doesn't function. It may, it may even do so quite well. Yet from the prespective of the craftsman, they're still to be considered as imperfections.

Let's start to recognize the peculiarity that a fault from the one perspective is just a characteristic from another: I've seen a number of mouthpieces which where the favorites of their owners, musicians of name and fame, in which some imperfection or other could be discerned. The wooden mouthpiece might serve as an example. It tends to warp and thereby might produce a torsion in the facing. But this doesn't necessarily render it unusable. It depends on how well the curve of the facing is conserved in the process of warping. So the first question always is: «does this mouthpiece work for me?», and if not, well then, consult the list below.

I will start with three faults that might still produce a working mouthpiece and end with three that will surely lead to difficulties. The red lines indicate the faults under discussion.