Something about Stradivari violins. It is

still not sure what accounts for their sound.

According to a new study modern instruments

perform equally well.

http://www.pnas.org/content/111/20/7224.abstract

Stradivari's wood could have been infested

by fungi.

https://idw-online.de/de/news495117

Another idea is that in order to forestall

insect and fungi infestation Stradivari

treated the wood with chemicals like

borax and other salts.

http://www.eurekalert.org/pub_releases/2006-11/tau-ms112906.php

http://esciencenews.com/articles/2009/01/22/secrets.of.stradivarius.unique.violin.sound.revealed.texas.am.prof.says

https://www.newscientist.com/article/dn10686-why-do-stradivaris-violins-sound-sublime/

Somewhere I've read or heard that Stradivari

might have dissolved insects like crickets

in hot lye in order to obtain a lacquer.

No reference available, sorry.

Treating wood with steam is also

an option:

http://www.atmosafe.net/en/pdf/moisture-content/thermowood.html?filename=Thermowood.pdf

Regards,

Joachim

In re Stradavari violins:

The wood used included spruce for the top, willow for the internal blocks and linings, and maple for the back, ribs, and neck. There has been conjecture that this wood was treated with several types of minerals, including potassium borate (borax), sodium and potassium silicate, and vernice bianca, a varnish composed of gum arabic, honey, and egg white. Stradivari made his instruments using an inner form, unlike the French copyists, such as Vuillaume, who employed an outer form. It is clear from the number of forms throughout his career that he experimented with some of the dimensions of his instruments.[3]

A comparative study published in PLOS ONE in 2008[4] found no significant differences in median densities between modern and classical violins, or between classical violins from different origins; instead the survey of several modern and classical examples of violins highlighted a notable distinction when comparing density differentials. These results suggest that differences in density differentials in the material may have played a significant role in the sound production of classical violins. A later survey, focused on comparing median densities in both classical and modern violin examples, questioned the role available materials may have played in sound production differences, though it made no comment on variations in density differentials.[5]

https://en.wikipedia.org/wiki/Stradivarius

Regards,

Bob Skiles

Dear Husni,

Another study I recently read (sorry, I cannot, now, find the citation) posited that the wood from which Stradivari made his instruments was denser due to the fact the trees he took it from had grown during the colder climate of the so-called "Little Ice Age" (Maunder Solar Minimum), and therefore, the growth rings of the trees were more closely packed together and, therefore,  the wood denser. The idea of the wood from the two different eras (Stradivari-vs-modern) being of differing densities was broached in the article cited above (but the underlying reason(s) for the differing densities was not suggested, that which I have supplied, here).

Regards,

Bob Skiles

Years ago I have faced such problem, I have treated the wood  first by acetic acid, then drying at controlled temperature hot air, finally, I painted the wood by resin solution 3-5% in alcohol) .

Hello Husni,

In principle, the wood for the table of lute family instruments is not varnished, in order to avoid addind mass to the very thin and resonant wood, because it is so thin than a coat of varnish could dampen the sound. The wood darkens naturally.

Sometimes, the resonant table is coloured with water based natural dyes, mostly when repairs need to be hidden.

The rest of the instrument, i.e. the neck, the head and the body, is usually varnished to protect the wood from getting dirty by contact with hands and with dust and dirt. It also provides an isolation from humidity and water and avoids deformations with the changes in relative humidity.

Many recipes exist for varnishing musical instuments: varnish can be made  either with spirit, turpentine or oils, to wich colors and resins are incorporated by cold or heating processes.

It is sometimes said that the wood itself could have been treated in the past in order to protect it form fire or from decay, or even to make it more resonant in making it lighter without loosing in rigidity, which would be good for acoustical properties : hypothesis are treatements by water based silica extracted from plants, or potash, potassium sulfate or even fungi, but none is very sure about that yet.

Anne

Very thin layer of natural resin solution (spray) was used to treat the surface of dried wood to avoid cracking and to improve resonance. I am talking here on the wooden body of Oud. not anything else. 

If you are interested, you can have a look on 11 oud (spelled "ud" or "oud" in the data base) kept in Museum collections in Europe: "Musical Instrument Museum Online" , here : http://www.mimo-international.com

The descriptions are still scarce at the moment.