Friday, December 20, 2019

A Special Kaiser Theorbo

After nearly two years I have finished an elaborate model of the Martin Kaiser theorbo, E.24, conserved in Musée de la musique, Paris.

Please take a look at the original Kaiser by using the MIMO portal. My story will make a lot more sense.

Enter "Martin Kaiser theorbo" in the search box and then click on the image of the lute. Be sure to click through all of the options. The images expand and can be scrolled through with the magnifying icon for a close detailed view. Keep this portal open while you read my post because I refer often to specific photos of the original lute.

The Kaiser model theorbo is not new to me. I have built over a dozen since 1997 but I never attempted to copy the detailed ivory work on the neck and extension. My clients have been young professional theorboists starting their careers so I always kept the aesthetic concept simple.

The story of this instrument is different. The client contacted me with the suggestion that I build a close copy of the Kaiser. He also wanted an instrument with low tension, low action, double stringing on the fretted strings, double tied frets and narrow spacing on the bridge and nut.

I have felt that I have drifted away from historical practice in the sense that modern players need to be heard and need to travel. I adjusted by adding a few tenths to the rib thickness or the belly and bars and adopted single stringing even though few of the many surviving historical theorbos are single strung.

I eagerly accepted the commission unaware that it would deplete my stock of black ebony, challenge  my skill and try my patience. But along the way I learned new skills and techniques and improvised on old ones. I felt I needed to do this. This is the story, in picture and words.

Where to start? I built the first few models of the theorbo using plans that I created from images of the instrument that you have seen on the museum's website and published measurements. A description of the instrument by Joël Dugot had also been published in Journal of the Lute Society of America, Volumes XVII & XVIII 1984 &1985.  Once I was able to examine the original ( March 2000) I improved the accuracy of my models.

All of my Kaiser models have been built on this mold although I have changed my technique recently. I no longer use the lines denoting the rib positions as the only means to determine the shape of each rib. Once I have fitted the edge of a new rib to the previous one I measure the distance to the edge rib of the bowl at various locations along the length of the bowl. These numbers are divided by the number of remaining ribs. I mark the results on the new rib and then plane off the excess material to the marks and then smooth them on a sanding board.

The widths of the ivory rib spacers of the original theorbo are not uniform. I recorded various widths  during my examination. I chose a median width of 2.2 mm. Visually this seems right as I compare it with photographs of the original. I also used white holly for the spacers throughout rather than ivory.

The green masking tape denotes the depth of the end cap and the two vertical lines on each side mark the two end points of the middle third of this important feature. This is a visual guide that helps me keep the ends of the ribs uniform as they pass under the end cap.

The original lute has a one piece ivory end cap with an incised black line (see the museum's photos). It is not original. I chose to use the standard early 17th century design composed of multiple pieces.

I usually build up my end caps by gluing them separately on the bowl one at a time and then cutting the finials. The work goes well but cutting the finials in place is tricky. Another technique, that I find awkward, is to construct the cap separately and glue it as one piece.

I tried a yet another method. I assembled the cap, fitting and tack gluing each piece separately on the bowl including the stepped top piece. The ends of the cap, not shown here, are left uneven. I planed the bottom edge of the cap flush with the bowl rim and then glued a piece of cotton cloth over the cap.

In the photo I have slipped a hot spatula between the bowl and the cap. The heat melts the weak glue joint and the cap comes off in one piece while also retaining its shape. I then cut the finials and glued the cap back onto the bowl using full strength glue.

The cloth support is then removed with warm water and a hot iron.


The procedure takes more time but I am happy with the result.

Before I release a new bowl from the mold  I cover it completely with clear plastic packing tape. If the bowl is too tight to the mold the tape will hold it all together while a little more force is applied. The rear end of the ribs are lightly glued to the mold but their integrity is protected by the end cap. A spatula slipped between the mold and the ribs releases the joint. I glue the front block to the front of the mold with three small drops of glue. These release when a spatula is forced into the joint.

With the plastic tape still protecting the bowl I use a curved scraper to smooth the inside of the bowl. The ribs joints are then covered with a light weight water color paper soaked in glue. The internal cap is spruce bent to shape and trimmed. A broad quarter moon shaped piece of water color paper covers the rear. This area is often the thinnest part of the bowl due to the amount of levelling that is necessary to fit the end cap and I think it needs extra protection. Only after these procedures are completed is the plastic tape removed.


I use quartered Canadian sitka spruce for the core of my necks. This is shaped and fitted to the front of the bowl. It is then covered with a hard, dense veneer in one of the many styles or designs that are represented on historical theorbos. The neck veneer of the original Kaiser is unique. It is composed of nearly 200 individual pieces of ebony and ivory arranged in chevrons.

Optical illusions created with black and white lines are popular mind-teasers. I spent a lot of time looking at photographs of the original design and decided that the white strips were slightly broader than the black even though they appear to be equal. I figured out the necessary dimensions and cut the strips of ebony and holly from larger stock.

 I laid out the design on a thin piece of plywood and using various templates to insure uniformity I glued the individual pieces of ebony and holly to the board using normal strength hot glue.

As I proceeded it became obvious that the slightest error in preparing the width of each piece would result in a misalignment of the mitred center joint.
To correct this, I constantly had to adjust the width of the individual pieces. It was a long, laborious process but the finished  result was satisfying.

Using the same technique as with the end cap I glued a single piece of cloth over the pattern. This remained in place while I planed off the plywood backing, bent the pattern to the curvature of the neck core and glued it to the neck core.

 I had second thoughts. My bending iron which is a 3 inch diameter metal pipe heated with a propane torch wasn't long enough to bend the entire pattern all at once which I thought was necessary to prevent the pattern from becoming distorted. I decided to split the pattern in half, left and right, and bend and glue separately. I also bevelled the abutting edges so the two halves would join without the possibility of a gap forming.

In the photo I am removing the cloth support after gluing the pattern to the neck core.


The result was fairly successful. I was unhappy with the alignment of several pieces so I cut them out and corrected the problem. 

I finished the neck with two white lines of holly along the edges of the chevrons and then two broader pieces of ebony that extended slightly beyond the edge of the neck core. The neck was then fitted to the bowl as shown in a previous photo.

The next step in my construction sequence was the preparation of the soundboard. The top is 6-year-old Swiss spruce. I had been working on it while I was assembling the neck veneer so it was nearly ready.

Large Italian theorbo soundboards are always impressive but I think the Kaiser soundboard is particularly harmonious due to the graceful flow of the contour, the proportions of the triple rose and the delicately thin bridge. The original Kaiser does not have a heart, but this instrument deserved one.

The Kaiser triple rose uses Leonardo's Knot as an elaborate center piece. I have always liked this design and what's better then cutting three of them?

The bridge is conserved separately from the instrument and I missed seeing it during my visit.
It is made of black ebony and is asymmetrical, larger on the bass side (13.6 mm front to back and 11 mm on the treble side) and higher on the bass side (8.5 and 7.4). The tips of the bridge are missing and whatever style they might have been can only be conjectured. The footprint of the original bridge is clearly visible and can be seen in the photographs of the instrument. To me the circular outline suggests a sunflower or rosebud. This style of finial is usually seen in paintings of 16th century lutes and survives on several surviving lutes. The top of the bridge is decorated with thirteen  6 pointed "stars" scribed into its top surface between courses. There are two scribed lines parallel to the front and back edges. There is no lip on the front edge of the bridge and the rear does not appear to be angled. I do not know if the rear face of the bridge is sculpted in any way to accommodate the string ends.

During my examination of the instrument I measured the footprint of the bridge that remained on the soundboard ( 14.2 / 11.8) and was surprised when I saw the published measurements some time later.
A very poor cleanup of the excess glue could explain this discrepancy but the lack of refinement in the construction of the bridge leads me to believe that it dates from a more recent time.

I constructed my bridge from European plum stained black and sealed with tung oil.  I created my "stars" with a small chisel, pressing it into the top of the bridge in a criss-cross fashion. I cut a string channel for the string ends to sit in.

The ebony veneered extension is tastefully decorated with triple bands of ivory/ebony/ivory and a single ivory line dividing both the face and rear veneers in half. Furthermore, on the face of the extension the triple bands are joined  in front of the ebony/ivory striped theorbo head by a crossover band with mitred corners.


On the rear the extension narrows so that all of the elements come together as nine equal bands.


The outermost bands of ivory wrap around the theorbo head and meet in a cross-over piece behind the nut.

Bending tight curves on a hot iron is a challenge. The thought occurred to me that I am substituting  a medium dense, fine grain wood for ivory and I remembered that ivory becomes pliable after soaking in white vinegar. So I cut a test strip of holly, submerged it in white vinegar (5% acetic acid by volume) for a couple of hours, and washed it off. After I allowed the strip to partially dry, it bent easily into the necessary shape with only finger pressure.

For the finished instrument I followed the same procedure but strapped the bent bands  onto the theorbo head with dressmakers elastic and allowed them to rest overnight.

I turn my pegs by hand without templates, shaping by eye and checking diameters with Vernier calipers. Many of the problems encountered with sticking pegs are caused by insufficient drying of the wood before they are turned. I use Castelo boxwood that I cut into turning squares. These are stored for at least a year. When I start a new lute I turn a set of squares to a rough shape. A while before I start applying the finish to the completed lute I turn the pegs to their near final shape. The heads and shanks are finished last and then fitted to the lute as part of the initial setup. If they are to be black, I ebonize them with a  process using quebracho extract and iron acetate. I use the process described in:  After the pegs have dried for several days I seal them with tung oil sealer.

The theorbo's bowl, neck and extension were varnished with several light coats of French polish applied in the traditional way. This was allowed to dry thoroughly and then was rubbed out with 4F Pumice stone. The soundboard received two coats of tung oil sealer, allowed to thoroughly dry and  was rubbed out by hand.

The string disposition: 8x1/6x2
The string lengths:  88.5/171 cm
Strung in gut
Information added 12/29/19
Instrument weight : 1970 grams ( fully strung)
Original instrument's weight: 1942 (without strings)
Instrument balances at the fourth fret 
All photographs by the author.