Month: February 2010

Now that the purfling is installed, we proceed to finish the outside arching of the back. The arching shape has a profound impact on the final tone of the instrument. Over the years I have settled on a particular arching shape for the Strad model that I find reliably produces an instrument with exceptional tone.

The first step is to rough-in the arching using the chisel.

We now move to finger planes and scrapers to refine the arching.

Finally, we use contour lines and scrapers to clean up irregularities in the arching shape.

There is a .75mm channel cut all around the instrument at the purfling. The Italians call this the “sgusciatura”.

Finally, the arching needs to be brought down a bit and blended into the sgusciatura. Again, contour lines are used to identify irregularities.

Using a low raking light, all irregularities are found and removed resulting in a perfect arching shape.

Next, we flip it over and hollow out the inside.

Now that the aqueous phase of varnishing is complete, it is time to prepare the ground. The purpose of the ground is to provide a smooth base for the colored varnish and to prevent the varnish from penetrating the wood.

The first step is to mix some pumice powder into some clear varnish. This is applied to the violin and then rubbed off. This is done twice with some curing time between coats. This step fills the pores of the wood and seals the surface.

Next a thin coat of clear varnish is applied. After it cures, the violin is rubbed down. The ground is now finished.

Next we apply the first color coat.

Now that the outline is established and the purfling platform is made, it is time to purfle the back. Purfling is one of the more demanding tasks in violin making. The purfling channel is cut by hand and must fit the purfling exactly all around the instrument. The purfling strips must be bent and cut to form a perfect miter at the corners.

The first task is to mark the purfling channel with a purfling tool. This tool scribes two lines 1.3 mm apart and 4mm in from the edge of the back.

Next, with a very sharp knife and a purfling picker, the channel is cut slightly more than 2mm deep.

Finally the strips of purfling are bent and cut to length. The miters are formed in the corners. The pieces are glued into place.

Next we finish the outside shape of theback.

Now that we have the back joined, we need to draw and cut the outline and establish a platform for the purfling.

We draw the outline by clamping the rib assembly on the back and tracing the rib outline about 3mm proud.

The outline is then cut out.

Now, obviously we have an excessive amount of unneeded wood. Before finishing the outline and establishing the purfling platform, we will rough in the arching.

Finally we finish the outline exactly and establish a purfling platform a little more than 4mm thick all around the back. The back is now ready to be purfled.