|
|
 |
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
Seasoning Violin Wood
1.Seasoning :
Wood that has been newly converted from a Log (Green Wood) – contains a
very high percentage of moisture. The Cell walls of the wood are
saturated and the free water is contained within the cell cavities.
Seasoning the wood is the process of removing the free water from the cell
cavities and also much of the moisture from the cell walls.
This process must be begun within a week of the wood being converted
( Felled), otherwise the wood is likely to rot because of the fungal growth.
As the wood dries , the free water is lost from the call cavities until only the
cell walls contain moisture.
This is termed the “ FIBRE SATURATION POINT ”.(F.S.P.)
and occurs at about 30% moisture content, depending on the species.
|
|
|
 |
|
|
( OD=Oven Dried KD= Kiln Dried AD= Air Dried )
It is when the moisture starts to be lost from the cell walls that the shrinkage
begins. The loss of water will stop when it is in balance with the humidity of
the surrounding environment.
This is known as the “EQUILIBRIUM MOISTURE CONTENT “(E.M.C.).
|
|
|
 |
|
|
For wood to be used for making instruments (With Spruce and Maple) , it
must be kept indoors in a heated room.
However, the difference in moisture content, between the cells and the
outside air “ VAPOUR GRADIENT “(V.G.) , must be brought to the
(E.M.C.) gradually otherwise many deforming side-effects will occur.
Bowing (Curvature along the face of the board)
Springing (Curvature along the edge of the board, where face remains flat.)
Winding (Twisting of the board)
Cupping (Curvature across width of board)
Splitting (Splits that develop along the grain of the wood)
Collapse (Cells collapse)
Case hardened ( Inside of the board is Dry but moisture is trapped in the
centre cells of the wood. When the board is resawn it will tend to twist)
|
|
|
|
 |
|
|
( Defects in the Wood are related to the direction of annular growth )
For most Hardwoods and therefore Maple, it takes about 1 YEAR to dry every
25mm (1 inch) thickness.
For most Softwoods , therefore Spruce ; it takes about 6 months to dry every
25mm (1 inch) thickness.
This time scale is based on the AirDrying method of Seasoning; however ; this
method will only reduce the wood moisture content to around 14% to 16% .
Therefore; further drying time is necessary which will take place indoors.
The total time needed for seasoning boards of thickness 35mm is about
3 years for Spruce and 5 years for Maple.
The other reasons why proper seasoning is necessary are as follows;
(i) Dry timber is easier to work with than very moist timber.
(ii) Moist timber will not readily accept glue., dyes, pigment, or varnish.
(iii) Moist timber will warp and deflect during the drying process.
(iv) In general dry timber is stronger and stiffer than wet timber.
|
|
|
Humidity in the Violin WorkShop
For Violin Plate Tuning it would be ideal ,(If the World were so easy to control)
to have the Workshop both Temperature and Humidity controlled.
Preferable humidity control would be:-
50% Relative humidity with temperature between 15deg.C to 25deg.
The Moisture Content (% Oven dry weight) of violin woods after conditioning
at 25deg.C at various relative Humidity.
Relative Humidity
Year & Wood type 15% 33% 65%
------------------------- ---------- -------- ----------
1756 Spruce 3.28 6.27 11.28
1900 Spruce 3.45 6.38 11.72
1976 Spruce 3.41 6.55 11.95
1936 Maple (unvarnished) 2.95 5.75 10.65
1936 Maple (varnished on 3.12 5.80 10.41
one side)
1976 Maple 3.18 5.99 11.06
( information by Rex Thompson )
“ The Effects of variation of Relative Humidity on the moisture Content of
Seasoned timber by Rex Thompson.
The variation in moisture content of old seasoned timber and relatively New
wood, when conditioned at the same Relative Humidity, is measurable, with
the old wood holding up to 1% less moisture than the New wood.
This slight difference in moisture content of violin wood at the same relative
humidity and temperature may be significant. Further work is required in order
to reach definite conclusions. “
|
|
|
Climate Effects on Violin Wood and its
Mechanical & Acoustic properties:-
The varying climate has a measurable effect on the Violin Wood dimensions.
Experiments carried out by physicist Jurgen Lehmann have shown the following
dimensional changes to prepared samples.
These samples were dried at 50 deg.C and stored at 50% Relative humidity at 23 deg.C
The samples were measured and then places in storage at 90% Relative humidity at 23 deg.C with the following results:-
(i) Measurements along the Grain increased by less than 1%
(ii) Measurements Perpendicular to the Grain and parallel to the radius (across
the front of the violin) increased by 4%
(iii) Measurements Perpendicular to the Grain and to the radius ( into the
thickness of the plate) increased by 10%
The results suggest that a violin Front at 25% Relative Humidity will be 3mm
thick and at 70% relative Humidity will be 3.15mm thick.
This raises many difficult questions over the measurements of great
instruments of the Italian Masters, and what thickness contemporary makers
should follow as guides to recreate the acoustic properties of these old Italian Master instruments.
The Stiffness of the wood in the violin has a great effect on the resonance.
Wetter wood is less stiff :-
Wetter wood is higher in density :-
At 90% to 100% humidity the spruce wood is 15% to 16% more dense
than in its dry state (approx. 50% humidity).
In practicle terms for the violin maker a 345Hz resonance in a dry instrument,
will be found near 295Hz in the same Wet instrument.
|
|
 |
|
|
( “Information by physicist Jurgen Lehmann :- As the Humidity increases,
the Frequency of the ring tone and the mass of the Violin ‘Plate increases.
this causes dramatic changes in the sound of the Instrument.
The Response of the Violin depends on the Mechanical dampening of the Wood.
As the Mass of the Violin Plate increases with the Rising Humidity, the Mechanical
Dampening of the violin Plate will Increase too. “)
This demonstrates one of the varying factors which dramatically influences the
Acoustic properties of the Violin, and highlights the Moisture content in the
Violin wood and its effects on the Acoustic Output of the Instrument.
|
|
“ Estimates of time allowed for wood seasoning:- by John Topham
Dentrochronological studies allow us to make some general conclusions about the time
allowed for wood seasoning in classical instruments. The time period between the youngest
ring and the attributed date is determined by two factors:-
Seasoning time before manufacture and
Removal of some of the outer most rings during the planing process prior to joining the Front.
This number varies widely, from a minimum of 3 years for some instruments by Guarneri del
Gesu to several tens of years for most of the other makers.
The frequent short intervals between the youngest ring, and date of manufacture suggest that
Cremonese makers made no systematic attempt to remove sapwood. the Short intervals also
indicate that in many cases it was not thought important to allow a long seasoning period.
Guarneri del Gesu has a reputation as hasty and not overly careful workman and perhaps the
short seasoning time is not unexpected. However numerous instruments by Stradivari seem to be
madewith rather young wood. The interval between the youngest ring and the date of manufacture
of 79 Stradivari instruments varies widely from 3 yrs to 60 yrs with 14 instruments having an
interval between 7 yrs to 15 yrs . This and other evidence suggests that extended seasoning
periods were not considered important by the classical makers. “
|
|
2. Grain Structure:
The mass of the woods cell structure constitutes the “Grain” of the wood,
which follows the main axis of the tree’s trunk. The nature of the
grain is determined by the (Cellular specialization) degree of orientation, and
environmental factors;
notably Seasonal weather, (Spring, Summer / Autumn, Winter)
and available nutrients, Oils ,Resins, and minerals, also contribute towards
density.
|
|
Certain Species of Pine ( Family Spicerae) for example
“ Picea Abies” (European Spruce) & “Picea Stichensis” (Sitka Spruce), are
ideal for the violin Front plate. Selected sound boards have to meet specific physical criteria which exhibit ideal characteristics of,
(i) Strength; (ii) Flexability; and (iii) Density
In order to exhibit excellent sound amplification.
Much of the tree grows very straight. This “ Straight “characteristic Growth, in particular the straight Late growth , (which are more dense than the early
growth , and are the principle vibration conductor), distribute the sound efficiently across the surface of the Violin front Plate.
For the violin a grain width of approx. 1mm is typical between the late growth
rings and the early growth rings, from the centre line accross most of the
Violin Front plate, widening out towards the edge.
( The increased grain width towards the edge provides extra flexibility so that
the Violin front can full fill its role well as a diaphragm.)
|
|
The density which is typical for the Violin fronts in
“ Picea Abies” (European Spruce) is around 470 Kg/M³ at 15% moisture
content.
Also in ,
“Picea Stichensis” (Sitka Spruce),) is around 430 Kg/M³ at 15% moisture
content.
The wood for the Front should be Quarter sawn for maximum strength with
Medullary Rays parallel to the top of the ribs.
The wide edge of the Quarter Sawn Wedge must also run parallel to the Grain.
Violin Wood Selected for the back of an instrument, must be a much harder,
rigid wood than that for the Front (Belly); however , still having the necessary
degree of flexibility and density.
Maple of the (Family Aceraceae) , for example
“ Acer Platenoides “ ( Bosnian or European Maple) and the density which is
Typical for this is 660Kg /M³ at 12% moisture content..
Maple used for instrument making has a certain amount of “ Flame ” to a
greater or lesser degree, an optical effect caused by the different angles of
reflection of light caused by the wavy pattern (the changes of orientation ) in
which the “Trachieds” were laid down.
Flame does not appear to have an adverse effect on the sound of an
instrument, though figured wood is weaker than plain wood and more difficult
to work.
There are other woods with similar suitable characteristics which could be used for the back.
Popular (“Populus Canadensis “)
- Black Italian Popular has a Density of 450Kg /M³ at 12% moisture content..
However , Maple is generally deemed better acoustically , and looks more attractive .
|
|
|
|
 |
|
|
|
Medway Cottage, Main Street, Youlgreave, DE45 1UW, Derbyshire, England. (0044) 01629-630099
All information on the Rocheviolins website is the copyright of Brian Roche.
|
|
