Wednesday, December 28, 2016

Gaetano Guadagnini Restoration - The Conclusion

Here is a photo of the Gaetano Guadagnini 1831 guitar after I finished its restoration. In my last post, after a brief introduction and a description of its condition, I used nearly the entire post to demonstrate and explain the internal blocking and shimming of the numerous cracks in the soundboard. Since there were so many cracks I couldn't help but wonder whether the guitar would regain anything of its former character. My goal was to return this interesting and important instrument by a member of the famous Guadagnini family to its rightful place on the concert stage in the hands of a fine musician.

The bridge is not only a prominent feature of the guitar it is also an integral part of the barring system of the soundboard.  The bottom of the bridge is contoured to fit the high arch of the soundboard and its unusual size (225mm x 14mm x 20mm) stabilizes the soundboard arch and moderates the soundboard vibrations in the same way that an internal bar does. I needed to take particular care in re-gluing it.

Clamping the bridge was going to be difficult because  pressure would be exerted unevenly on on the front half of the bridge leaving the important rear gluing surface unsecured. I devised a caul to solve this problem. Bridge clamps placed through the sound hole could now be centered on the caul. Others clamps were placed on the bridge wings. An arched  caul provided necessary support internally. Clamping pressure was exerted equally across the length of the bridge ensuring a good bond.

Now I could turn my attention to the back. I had taken the three bars off the back and those had to be carefully replaced in exactly their former location. I had previously marked their location so that went smoothly.

Even though I had retained the guitar in a collar (see previous post) in an attempt to keep the contour of the side ribs stationary they splayed out slightly. When I tried to align the back it no longer fit. I wasn't completely surprised. The bass side rib bowed in slightly at the waist but out at the upper bout - a perplexing and difficult situation. I wasn't convinced that normal clamping pressure would hold everything in the correct alignment so I made a special clamping jig that spanned the width of the upper bout.

On the treble side upper bout it fit flat against the side rib and was held in place with a vertical screw clamp.

The bass side of the clamp was made to exert pressure near the gluing joint. This arrangement pushed the side rib into alignment while the neighboring clamps held the joint together.

You'll notice that the wooden clamp feet point in different directions. I made the clamps this way on purpose. The feet fit more or less loosely on the screw rods allowing each foot to conform to the any arched surface. Turned sideways the foot is more rigid and less of its surface is in contact with the subject.

It was clear to me the gluing operation would take a lot of time. Too much really so I decided to do the work in stages. First, I clamped everything in position without glue. Then starting at the neck joint - this ensured that the proper neck angle would be preserved - I released a few clamps and inserted hot hide glue with a brush, knife or artist spatula.  Once the clamps were re-applied I moved along to the next area, one side then the other. I treated the upper bout, waist and lower bout as separate areas. The technique worked almost perfectly. There were several minor areas where the back overhung the ribs. Whether the back or sides changed shape or shifted or I erred is difficult to know - probably a bit of each.

Originally, the peghead was fitted with wood tuning pegs but these had been replaced at an earlier date with mechanical tuners as shown.
The peghead angle is 20°.
I removed the metal tuners and plugged their  holes as shown. The holes for the posts of the metal tuners were different than Guadagnini's wood pegs so there was some over-lapping of holes which I thought might cause problems. To avoid this I laid out a slightly different peg spacing in order to avoid drilling through an area that was already weakened by over-lapping plugs.  Also, the gears on the metal tuners were mounted with protruding lugs that left deep ugly holes in the peghead wood. I filled these with a mixture of fine ebony filings and cold fish glue.

I sanded the rear of the peghead smooth and refinished it with shellac dissolved alcohol blackened with aniline dye. The end grain of the wood plugs resisted the new finish and many applications of the shellac solution were required. I used a chisel tipped artist brush to build up enough thickness of polish that could be levelled. Then I switched to a regular French polishing technique to finish the job.

The photo is of the finished peghead. The tuners are a planetary type peg.

Although I had finished all of the major restoration work there were a few things to tidy up. Two of the inlaid ivory frets were broken with fragments missing (the 9th and 11th), so I decided to replace these with ones I made using bone saddle material. I also levelled the frets and re-crowned them using typical fretting tools.

I did not clean the top before I started working on the cracks because doing so would have forced grime into the open wood, staining the edges of the cracks and making the subsequent shims even more obvious. Cleaning the top was part of my plan to blend the lighter color of the shims with the original color of the top. I dampened a new shop rag with water as hot as my bare hands could tolerate, wrung it out quickly but throughly, and wiped it over the top. Then I burnished the top dry with a wool polishing cloth. Since the wood I used for the shims had darkened with age this final procedure produced a good looking aged patina.

Note* I would not have used such hot water had I not been sure that all parts of the top were sound and secure.

After I finished re-gluing the back a few areas overhung the side ribs as previously mentioned. Levelling these with the side ribs removed the original finish. In this photo the finish had worn off the bass bout through years of playing. Since that was part of the guitar's story I left that alone as well as other wear marks. Closer to the neck was an area that my work disturbed. I renewed the finish by making a thick glaze that could be brushed on the bare wood in one coat.

Glaze was applied to the edge of the back in this area too

I mixed about a 3mm length of burnt sienna oil pigment squeezed from the tube with an equal amount by volume of spar oil varnish and several drops of cobalt dryer. I brushed this on with as little overbrushing as possible and allowed it to dry for several days. Then I sanded out any heavy brush marks with 600 paper and applied a thin wash of a shellac solution.

That finishes my description of the restoration of this splendid guitar. Here are two final views.

All photos by the author.

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