Cremonese edgework starts from edge thickness. Almost invariably, the thickness of the unworn edge on a Cremonese violin (in the upper and lower bouts, not the corners and c-bouts, which run by different rules) is equal to or slightly less than the distance from the edge to the purfling. This leads to the easy conclusion that the two are somehow related, and the cause seems clear: they were both set with the same tool. A single-bladed purfling cutter, such as the still-extant one of Stradivari, can do double duty: not only can it be used to cut the purfling groove; it also can serve to cut in from the side of a plate, to establish the finished edge thickness. I often do this instead of using my drill press, and of all the hand tool methods of finishing the edge thickness, it is by far the fastest and easiest. (This method of working establishes a band of square cross-section edge outside the purfling, which begs to be rounded into a perfectly circular edge, but that’s not part of this discussion.)
Having located the position of the purfling, consider what happens at the corners, where the purfling lines meet from different directions. Photo A is a corner of one of my del Gesu model violins.
This is a typical corner form for a earlier instrument (later del Gesu corners differ from this in an number of ways). It’s about 6.8mm across the end. The crest of the edge is about 1/3 of the way in, more or less, from the outer edge. The purfling meets a bit farther inside the end of the corner than a Strad would because though the del Gesu purfling is set in about the same distance from the edge, the corner is smaller at the end. The two critical factors in getting purfling to end properly at the corners, rather than too soon, or going out through the end of the corner, are the width of the corner, and the inset of the purfling.
Look at the crest of the edge, as it approaches the corner from either direction. You can see that if the corner were much narrower the two crests would meet in one point (as the purfling does), but as it is, they don’t. This is an exaggerated illustration of what happens if you set the purfling too close to the edge, or make the corners too wide: the purfling never meets at the corner at all. If the purfling were 4mm in, and the corner 8mm wide at the end, the purfling point would be formed exactly at the end of the corner, and this isn’t good, either. The end of the purfling joint should always be within the boundary of the crest on the end of the corner—in fact it shouldn’t touch it at all (the bee-sting in my example is a bit on the long side—that period of del Gesu wouldn’t really have one, so the point would be ever further from the end of the corner, normally, because of the small corner size of the del Gesu model), and this is why the largest Cremonese corner you’ll ever see is around 7.5mm across the end. Many are smaller.
Stradivari and other Amati school makers drifted the outer bout purfling inwards a bit as it approached the corner, and this caused the purfling joint to fall farther from the end of the corner than it natrually would, allowing them to extend the purfling for a bit of extra distance in an elegant bee-sting. I also think it allowed for a bit of wear on the outside side of the corner before it started to look ugly in its relationship to the purfling. Del Gesu didn’t do this, and his purfling consequently looks a bit like it’s been smashed together at the end in later examples, and usually follows the outside line of the corner more precisely. Makers from other cities often didn’t think about any of this at all, and their purfling commonly does unfortunate things like running out the ends of their corners. Attention to all of the tiniest details is one of the things that makes Cremonese violins so attractive and interesting.
How the scoop of the edge is integrated into the corner shape is another interesting problem that hardly gets considered at all. In the previous photo you can see that the scoop is limited at the outside by the crest around the edge. (On the inside we don’t have to worry about anything except blending it in with the arching, and attempting accuracy to the model we’re following as regards the exact width and contour of the scoop.) This crest continues around the end of the corner, and mimics the outline of the corner itself, exactly. Since the scoop is quite wide and shallow, relative to the corner width, when it approaches the closing outline of the corner, there’s a decision to be made: to fit within the boundaries defined by the crest as it surrounds the scoop towards the point of the corner, either the contour of the scoop has to become tighter (saying the same depth, but becoming narrower and more tightly curved, as if it was cut with a deeper scoop of gouge) as it enters the corner, or the contour can stay the same (fitting the same gouge), but it cannot remain at the same depth. The Cremonese approach used by Stradivari, and by del Gesu in the period for this corner, was to keep the same scoop, but make it shallower as it approached the end of the corner. That’s what photo B shows.
The alternative, changing the scoop, results in a dug out sort of corner, lacking the elegance of the Cremonese solution.
Later del Gesus deal with this spot differently, in a method which is easier to accomplish, but which leaves a deep ugly trench at the inside of the purfling point going straight in from the corner. This usually has been attributed to the use of a shallow gouge cut made inward from the end of the point, but I believe the solution is actually much simpler, and sensible. Rather than attempting to scrape out his scoop in the edge beyond the purfling, I believe that later del Gesus are only gouged in this area and left raw from the gouge. When the gouge marks coming from either direction meet just past the tip of the purfling joint, the resulting junction is a depression that resembles the mark that would be left if a canoe were run aground there—a cut shaped like the prow of a boat, with a keel mark left in the wood bisecting the corner—the mark that others have mistaken for a gouge cut.