The Leonardo Tests


We’ve planned to make two type of tests with different sort of wood samples.

  1. Darkening different oak samples with ammonium – fuming
  2. Crack test with the non-tropical and tropical wood samples from the leonardo guitar research project  (this test is cancelled and rearranged as a fuming test with tannin acid ,because of the diversity of the samples according to the grain direction and sizes cannot make any conclusion and the results will be not significant)


The Fuming experiment


Ammonia fuming is a wood finishing process that darkens wood and brings out the grain pattern. Unlike most other finishing techniques, the fuming process is colouring the wood all the way through instead of only superficially. It consists of exposing the wood to fumes from a strong aqueous solution ammonium hydroxide which reacts with the tannins in the wood. The process works best on white oak because of the high tannin content of this wood. Fumed oak is also called smoked oak. Other species may also be fumed but usually will not darken as much as white oak.

The wood to be fumed is placed in a sealed chamber with all the surfaces to be fumed exposed to freely circulating air. A large shallow container of ammonium hydroxide solution is placed on the floor of the chamber and the chamber is sealed. If the chamber is large or the fuming is to be done for a long time then more than one container may be provided or the ammonia may be replenished during the process. The fuming time depends on the amount of darkening required, the size of the chamber, and the strength of the ammonia used. It is usual to oil the wood after fuming to fully bring out the effect.

Fuming has an advantage over staining in that it does not obscure the grain, it just darkens it. Unlike staining, there is no possibility of blotches or runs. Fuming is also colorfast. Fuming has the disadvantage that it is not a very precise process. Different batches of wood will react to fuming differently. For this reason wood that is to be fumed for a particular project is often taken from the same tree. Even so, boards from the same tree, and even different regions of the same board, can have a noticeably different color. Where a consistent color is important, staining or dyeing may be better options.

Fuming has some inconvenient safety issues. The solution of ammonium hydroxide used is much stronger (26% to 30%) than in household ammonia and is corrosive. The fuming must be done in an enclosed sealed chamber. Ammonia splashes can burn skin and the fumes can cause burns to eyes and lungs. Operators need to wear gas masks, gloves and eye protection.

The darkening of the color relies on the ammonia reacting with tannins in the wood. The process is most usually applied to white oak as this wood has a high tannin content. Red oak may turn greenish rather than deep brown. Other species may not darken so noticeably as white oak, or at all, depending on the tannin content. The effect of fuming can be enhanced in non-tannic woods by applying a coat of tannic acid to the surface before fuming.”


 -Test 1.-

We had 5 types of oak samples:

  • Already smoked oak (S)
  • Holm oak – Quercus ilex (E)
  • oak from floor (F)
  • oak from table (T)
  • Local oak (L)

All these samples were prepared and numbered before by Amélie. For the relatively small plastic container we created a 3 level compartment to hold above the samples from the ammonium. After the box have been loaded with the wood pieces, we filled the bottom of the container with the 25% ammonium hydroxide  and closed it with the lid, and an extra plastic bag added around to insure air tightness.

After  1, 6, 19, 44, 68, 92 hours we took out one sample from each type of the oaks and compared them with the control samples. We only took out samples when we noticed a change of colour, which explains the irregular time intervals of take outs.



 -Test 2.-


The other test we had is with the wood samples from the leonardo guitars. After they have been cutted and marked, we made 3 groups:

  1. control samples without any treatment
  2. samples with fuming
  3. samples with tannin acid and fuming

We used the following mixture to submerge the samples of 3. for 22 hours in tannin acid and let them dry an extra 22 hours before fuming :

  • 400ml 96% alcohol
  • 4 tablespoon of tannin acid powder

During the tannin acid treatment we shaked the compound regularly for the optimal effect.

Both tests are still running, results and conclusions will come later!



Soria is a province of central Spain, in the eastern part of the autonomous community of Castil and Leon. Most of the province is in the mountainous Sistema Ibérico area.

It is bordered by the provinces of La Rioja, Zaragoza, Guadalajara,Segovia and Burgos . Soria is the least populous of all of Spain’s provinces, with a density of around 9 inhabitants/km²—one of the lowest in the European Union.


Map of Spain with Soria highlighted


The places we spend most of the time during our staying was of course ‘Chavaler‘ and ‘Espejo de Tera’. Football is very present in this places, even in our staying we could play table football witch was nice, to get active again after the siesta.

Between the two villages you have a nice route, what takes 50 minutes to walk from the one village to the other. It’s a little rough by car but it’s saver to ride on when it’s slippery on the road during the winter. (when it’s raining and /or snowing when it’s freezing)


On our day off we decided to go look around to the places Thomas suggested us to see. Molinos del Duero, Duruelo de la Sierra,…


 playa Pita


Duruelo de la Sierra


Cañon del rio lobos Natural Park



La Fuentona de Muriel




Visiting Madinter


On friday 19/02 we visited ‘Madinter wood for music’, only  2,5 hours from our staying. In Spain of course. It’s a young company, only 15 years old with ambition. Stationed into ‘la Sierra de Madrid, Cerceda’

We’ve been welcomed very friendly by the workers and their employers. Cedric had the privilege to give us first a presentation with a slide show about Madinter. “What is their Vision, Misson and Value.”

They’re proud about ‘The Cameroon Project’ not only because they own the factory and gives them the absolute control* about the high-quality ebony, but also for the 80 inhabitants who work there for them. (* Their sustainable and responsible forest economy.)

After the slide show he showed us also the ‘Blackwood tek’ a fast New Zealand growing Pinus radiata who has large growth rings, which is essential for the subsequent impregnation and compression process to create black wood . We had the opportunity to inspect a few examples with and without linseed oil. It smell like mushroom and it’s hard, that’s for sure.

Then it was time to visit the factory by itself, … the boss guided us around.  Most time of the year he travels around the world. From Spain to Cameroon, to India or to Romania. He told us that some of his employees where visiting Cameroon because it is important that everyone in the company knows, and has a contact with each other. They’re one company.

¡Hola Spain!


The last two weeks of February we’ve (Sandra and Dániel)  had an internship by Thomas Holt. We arrived late in the evening  at Thomas workshop in ‘Espejo de Tera’, where we’ve being expected. He welcomed us very friendly and proposed to guided us to our sleeping place, because of the long journey we had made by car and it was late after all. Our sleeping place was in the next little village called ‘Chavaler’, a nice warm big place.






The first morning we’ve being picked up by Thomas, to have a coffee with a typical spanish breakfast in a local café at Garray. A moment to become acquainted with each other, and becoming acquainted with what was comming up the next days. Working efficient , to exchange knowledge, the visit to Madinter on friday, and of course about the leonardo project tests.

After we’ve been introduced to the siesta we started in the workshop.




Cut the frets with the pliers until the edge of the fretboard, file the fret flush till the edge of the fingerboard, first straight then in an angle. Fill the gaps under the frets with black shellac (gomalac). Then use a fine and very straight sandingblock made for the purpose in the same angle. Rounding the frets with a triangle file. Clean the fretboard and the frets with stealwool.




Thomas glues the bridge on the top before porefilling and uses paper and masking tape to protect the top. First clean the pores with a soft brush also in the bone. Seal the bone on the bridge with cellulose. After drying the porefilling can start.


Top and Neck


Draw the shape with the plantilla on top and cut it with the bandsaw. Then make a little mark with a saw in both extremes of the center line. These marks unlike  pencil marks will not disappear when working the thickness of the top.

Cut one millimeter slice from the neck with the bandsaw. Take the slice and break it careful by following the grain. This gives you the information about the grain in the wood. Draw the information on the wood. It’s usefull later to choose your neck or heel.