Questions on Musical instrument finishing

[CHJ]

Stolen from Cocobolo finishing thread

I have two clarinets made of cocobolo. They are shellacked on the inside, and oiled with e.g. tung or almond oil on the outside. No problems for either.

Sorry, straying off topic, but just realised I've never considered the reaction of wooden wind instruments to breathing air moisture, is it a problem necessitating the sealing of the inner airways or is the fact that denser woods are used enough?

 

[MusicMan]

Chas, it's a very significant problem, and the solutions are still contentious! What is well established is that only certain woods are suitable. Overall density has to be high, typically 1.2+ g/cm^3. Porosity has to be low, and it needs to be diffuse-porous not ring porous. Of European woods, only maple, box and some fruitwoods are suitable. Oak, ash, elder, pine etc are useless. Tropical woods are popular, especially any of the Dalbergia species, which are now all on the CITES II index. The biggest use now is of dalbergia melanoxylon (aka blackwood, grenadilla, mpingo) for which intense conservation/sustainability projects exist. Powdered grenadilla in resin surprisingly works quite well.

Treatments to the interior are oil or shellac, oil being the most common. Grenadilla is highly impervious (unlike boxwood and fruitwood) and it is debatable whether oil has much effect. Most makers and repairers think that some oil helps to get the right surface texture. Tung and almond oil are the favourites, or unboiled linseed if you have lots of time. The best way is to immerse the instrument in a cylinder of oil and then pull a vacuum on it - that is really effective.

Despite all, there is usually some movement with humidity. I used to commute twice a year between UK and Colorado with some instruments, and the change from 60% to 20% RH usually altered a few dimensions, necessitating adjustments to keywork.

I haven't made measurements, but my very strong impression was that the movement in humidity changes decreased down over many years, and at 20 years old my cocobolo instruments have virtually stopped moving. I have also found this in old (250 year) oak in furniture for restoration. One bureau had shrunk across the grain by about 1.5 cm over the centuries. 20 years in an uninsulated and unheated shed with UK humidity did not reverse this. I think most of our experience and received wisdom on wood movement comes from relatively short timescales of a few years, ten at the most.

The major high-end custom clarinet makers will season their grenadilla wood in rough-turned, rough-bored form, turning 90 degrees every 3 months, for 10 years. I've seen this at Wurlitzer in Germany. Then they will make the clarinet and sell it. The user is supposed to return it after five years use for a final skim to dimension.

Keith

 

[CHJ]

That's very interesting Keith, thanks for the detailed reply.

 

[Sgian Dubh]

I haven't made measurements, but my very strong impression was that the movement in humidity changes decreased down over many years, and at 20 years old my cocobolo instruments have virtually stopped moving. I have also found this in old (250 year) oak in furniture for restoration. One bureau had shrunk across the grain by about 1.5 cm over the centuries. 20 years in an uninsulated and unheated shed with UK humidity did not reverse this. I think most of our experience and received wisdom on wood movement comes from relatively short timescales of a few years, ten at the most. Keith

Keith, I strongly suspect you are not mistaken in your observations. I think you may be able to read more on this topic than the quotation below in your copy of Cut & Dried - I think you have a copy anyway, pp 87 - 88, Section 6.13. Slainte.

"Research into this phenomenon is limited, an example is the paper by Esteban et al (2004, pp 275 -- 284) in which they describe experiments undertaken to better understand it. The authors discuss the changes that take place within wood as it undergoes cycles of gaining and losing moisture. They describe changes in wood’s microstructure, essentially chemical in nature leading to 'hygroscopic and dimensional ageing of wood ... [resulting in a] loss of response of wood in relation to hygrothermal changes' (p 276). In other words, old dry wood which has been through many seasonal cycles of adsorbing and desorbing moisture becomes less hygroscopic with time, and less responsive to variations in temperature and relative humidity."

 

[CHJ]

I have several panels of 3/4- 1" Oak retrieved from furniture my Father made in the 1930's, 2ft wide panels (shellac/French polish finished) had shrunk width wise some 3/8" when dismantled in 2005.
Stored in the garage awaiting the inspiration to make something significant with it, and subject to seasonal humidity changes and regular wet car storage they have not shown any marked movement or change in moisture content with simple meter.

 

[MusicMan]

I haven't made measurements, but my very strong impression was that the movement in humidity changes decreased down over many years, and at 20 years old my cocobolo instruments have virtually stopped moving. I have also found this in old (250 year) oak in furniture for restoration. One bureau had shrunk across the grain by about 1.5 cm over the centuries. 20 years in an uninsulated and unheated shed with UK humidity did not reverse this. I think most of our experience and received wisdom on wood movement comes from relatively short timescales of a few years, ten at the most. Keith

Keith, I strongly suspect you are not mistaken in your observations. I think you may be able to read more on this topic than the quotation below in your copy of Cut & Dried - I think you have a copy anyway, pp 87 - 88, Section 6.13. Slainte.

"Research into this phenomenon is limited, an example is the paper by Esteban et al (2004, pp 275 -- 284) in which they describe experiments undertaken to better understand it. The authors discuss the changes that take place within wood as it undergoes cycles of gaining and losing moisture. They describe changes in wood’s microstructure, essentially chemical in nature leading to 'hygroscopic and dimensional ageing of wood ... [resulting in a] loss of response of wood in relation to hygrothermal changes' (p 276). In other words, old dry wood which has been through many seasonal cycles of adsorbing and desorbing moisture becomes less hygroscopic with time, and less responsive to variations in temperature and relative humidity."

Yes, I do have your book, Richard, but not studied it yet, That's a great reference and I shall follow it up. Many thanks. It is actually highly relevant to museum practices - there is always a conflict about permitting the playing of ancient instruments. It would be good to prove that they are stabler than one thought!

I also have some teak floorboards from about 1850 (ex St Mary's Hospital Paddington) and Oregon pine from Dover Naval Barracks, around the same date, which are incredibly stable.

best, Keith

 

[MusicMan]

Oh, another point about woodwind instruments. From observations made by the woodwind maker Daniel Bangham, and my own observations in studying hundreds of clarinets in museums, it appears that there is a common form of grain orientation in woodwinds. Many of the logs used for boxwood and grenadilla instruments were not huge in diameter. It appears that they were quartered, then an instrument was made out of each quarter, oriented so that the finger holes lay on a radius from the centre. In effect, therefore, they were all quarter-sawn, with just one billet per quarter.

 

[Sgian Dubh]

Yes, I do have your book, Richard, but not studied it yet, That's a great reference and I shall follow it up.

Keith, the Esteban source listed in the References and the Bibliography of Cut & Dried can still be found on the internet. Just type in the reference's full title of the paper, as well as the author's name. It's a bit of a dry and dusty read, but if you're into that sort of thing I think you may be able to use it to bolster any points you may want to make about old instrument wood stability. There are probably more scientific papers out there on the subject, if you care to look even deeper. Slainte.

 

[Droogs]

I have noticed over the years that pipers who play inherited (Great Grandads pipe etc) sets do seem to have less trouble getting them tuned than those of use who used newer ones do when we used to deploy or go on tour with the pipe band around the different temperate/tropical zones of the world. My pipes used to basically fall apart when I went to the middle east and I would have to rethread them continually while there. A good friend of mine though had pipes that were played supposedly at Cullodean and he never seemed to have a problem. Somea there's probably something in very old wood being much more stable, even to a near constant stream of moisture from breath

 

[profchris]

All I know is fretted instruments like guitars, but from that two things:

1. The reduction in humidity caused movement is real, known as hysteresis. What's not known is whether it's a function of pure age, or whether it requires repeated shrinkage and expansion cycles. All long seasoning seems to expose the wood to humidity cycles. After 50 years, maybe less, there is still movement but much, much less.

2. No finish is a humidity barrier, except maybe thick epoxy. All the others at best slow the uptake of moisture. So build on the basis that wood will move, for its first century at least!