The organ is truly a living instrument, consisting partly of organic materials which are sensitive to various factors. Therefore, a certain variety of decay may occur.
Alterations caused by climate
The organs are mainly installed in churches: Their atmosphere characteristically contrasts from very humid in winter to very dry in summer. Furthermore, in winter the atmosphere is undergoing significant temperature fluctuations (therefore significant relative humidity) between weekdays, when the building is not heated, to Sundays, when the heating system causes a sudden rise in temperature for the purpose of worship.
Wood is the principal organ component. As a hygroscopic material, it reacts strongly to these variations in temperature and humidity. Excessive humidity will cause the wood to swell, whereas a too dry atmosphere will cause its retraction. These movements can eventually cause cracks and bursts which adversely affect the operation of the instrument.
The metal which constitutes the pipes is less sensitive to those climate variations. However, excessive humidity, coupled to a phenomenon of mutual interaction between wood tannins and metal elements, may cause corrosion. A phenomenon called “tin leprosy” can affects pipes. Other lead items such as conveyancings can suffer from corrosion too. This corrosion, if left untreated, can lead to breakthroughs, or even to a complete disintegration of the metal.
Finally, very sudden changes in climate have adverse effects on the voicing of the organ: the pitch being related to the temperature of the air, these variations therefore tend to detune the stops.
About heating systems
In order to minimize damages due to climate, it is very important where possible to recommend a suitable heating system. It is thus better to avoid forced-air or radiant panelled heating systems. As they allow a rapid increase in the temperature of buildings, they are also the ones that cause the most brutal climate variations. One should therefore prefer heating systems that gradually increase the temperature, such as floor or electric heating.
Wood is besides sensitive to wood-borer and mould attacks. Wood is indeed a nutrient cellulose stock for the larvae of those insects, which can sometimes live for several years in the wood before moving to the adult stage. Wood-boring pests come in a wide variety: common furniture beetle, death-watch beetle, powder-post beetle and longhorn beetle are the main ones. Other insects like carpenter bees or termites can also damage wood.
The presence of an active infestation is revealed only once the larvae become adults, when they cut holes out of wood. These flight holes can therefore be revealing elements, particularly when fresh sawdust is found nearby. In every case, a wood-boring infestation requires a curative treatment so as to eradicate the larvae. We have selected the technique of diathermy (Hochfrequenztechnik), achieved by Agil, which has the advantage over anoxia to allow the quick treatment of large volumes.
Besides, wood and moreover animal glues that are used in the making of the instrument are nutrient sources for a wide range of microorganisms that grow mouldy. Their growth may weaken the wood too, because they feed on the cellulose and proteins found in the glue: the wood loses its cohesion and various types of rot can form (simultaneous white or cubical brown ones). A simple way to prevent the growth of microorganisms is to maintain a relative humidity below 70% and properly ventilate the building.
The alterations affecting an organ are numerous. It is imperative for us to regularly monitor our instruments. This allows us to control their good health and prevent any damage. These operations are usually performed by Yves Koenig, Roland Weiss or Julien Marchal.
Our service contracts provide that we achieve once a year the following interventions:
- Complete tuning of reed pipes and tuning correction of flue works
- Adjustements of the action.
So as to maintain an instrument in optimal condition it is advisable to regularly perform a refurbishing operation. Refurbishing shall ideally be repeated every ten years. At least it should be achieved once every twenty-five years. Refurbishing includes a series of operations:
- Removal of all pipes
- Dusting of case and pipes
- Insecticidal and biocidal treatment
- Airthightness review (soundboards, windtrunks, bellows)
- Replacement of wearing parts
- Action review
- Pipes refitting and voicing
- General tuning.