Taking care of your guitar
- The metal parts of the machines (worms, gear wheels) remain smooth-running with a drop of acidless oil once or twice a year (on the plastic string rollers or the wood drillings however no oil should be used).
- Occasionally it may be necessary to tighten the mounting screws of the baseplates.
- When changing strings the load on the top is retained if they are changed individually and successively, while the remaining ones stay in tune.
- Should it be necessary to remove them all at the same time (e.g. during long playing intermissions or transports) a dangerous one-sided tension load can be prevented by stringing them up and down symmetrically pairwise (that means e.g. first E-string and e-string, afterwards A-string and b-string, finally D-string and g-string).
- Knots at the ends of the nylon strings secure them against slipping through the bridge drillings.
- By wiping of the strings after playing (e.g. with a cotton cloth) humidity and dirt are removed. Thus the corrosion of the metal wound bass strings is reduced and their durability is extended.
- Sharp edges of nuts, saddles or frets can destroy the string. Occasionally it will be necessary to work these over.
- The polish should be protected against excessive exposure to the sun or other strong heat sources.
- Protective cotton cloths or soft leather rags help to avoid scratches by buttons, zippers etc. and a possible reaction of the shellac with the acid in perspiration.
- When changing strings a patch of leather placed at the lower edge of the bridge protects against nail scratches.
- To clean the polished surfaces normal household dust cloths may be used, or cotton cloths slightly dampened with warm water if heavily soiled. In that case however, the surfaces should be wiped off with a dry cloth afterwards, and no cleaning agents should be added to the warm water. Other polishes or cleaners must first be examined for their compatibility with shellac before they are used.
The many different shellac polishes are all based on shellac (resina laccae), a deposit on the branches of certain trees, e.g. fig-, hibiscus- and ficus- species, which are native to Thailand, India, Sumatra and other countries.
It is the dried secretion of different types of parasitic lac bugs (carteria lacca, coccus lacca). After their fertilisation the tiny wingless females attack the trees and pierce the branches in huge numbers (to produce 1 kg shellac about 300.000 bugs are necessary). By sucking they cause the plant to ooze a resinous sap which they eat. Through digestion it undergoes a chemical change and is secreted again. With this excrement the bugs construct cells similar in function to honeycombs in which they lay their eggs. The resin coats the branches totally with time and solidifies gradually to crusts, whereby most of the insects die. The larvae eat the honey-like nutrient with which the cells were filled, finally break out of them and leave to renew the cycle.
Suitable trees are cultivated in plantations and are harvested twice a year, i.e. their branches are struck with sticks in order to loosen the crusts which are then gathered. The so called sticklac (lacca in baculis, lacca in ramulis) is then crushed, sieved and repeatedly washed to remove impurities like dirt or parts of the plants and insects. The resulting product is known as seedlac (lacca in granis). Further refining by heat treatment, solvent extraction, filtration, bleaching by means of chemical additives and drying leads to the actual shellac.
Depending upon the kind of insects, trees, and refining methods it is avaiable in different grades with different chemical compositions (resin, waxes, oils, colour, etc.). To use it as a polish it is dissolved in denatured alcohol (ethanol, spiritus).
There exist several techniques to coat a wooden surface with shellac polish. Like other lacquers or varnishes it can be brushed or sprayed. The traditional and most suitable one in guitar construction is the so called French polishing. This means that shellac is applied in low concentration and quantity using a rubbing pad and specific rubbing motions. The pad is made up of wool or wadding wrapped with a piece of cotton or linen. The process is time and labour intensive and very delicate. Interrupted by long drying times the finish is build up by numerous thin layers of polish.
Shellac has several advantages compared with modern finishes which are mostly sprayed (nitro-cellulose, acrylic, polyester, etc.):
It can be applied very thin and evenly (under 0,1 millimetre thickness), and due to its components (waxes) it is more flexible. The coat can manage the changes in form and volume of wood (shrinking and swelling as a result of its hygroscopic characteristic) and it also strengthens and supports the oscillation of the top without hindrance.
A characteristic trait of traditional French polishing is the considerable pressure with which it has to be applied (depending on work step). Thus the shellac particles are compressed to a homogenous density which can not be achieved by brushing or spraying techniques (where particles adhere each other only lightly). This increases the bond and anchorage to the wood.
If the finish is damaged, e.g. by crack repairs, it often can be renewed or restored with little effort, since the existing lacquer substance is soluble again and new layers connect excellently to older ones.
Also its aesthetics, transparency, gloss, and natural impression exceeds the synthetic finishes. In addition as a natural product most grades are non-toxic (however this is not true with some chemically refined grades).
Unfortunately there are not only advantages. The resins and waxes which favour the flexibility also display a higher sensitivity to heat (melting point 60°-100°C depending upon grade) and to the acid present in perspiration, and are less hard, offering less protection against scratches and abrasion.
Some advice with regard to the handling of shellac polished guitars: If possible the finish should not come in contact with bare skin, except of the neck. The neck can be wiped off with a soft cloth after playing. Long extensive heat, e.g. by exposure of the sun, radiators or even continuous body heat should be avoided (soft leather rags or cloths can be underlayed in addition to the clothes).
Even with great care it may be necessary to restore the finish at intervals of several years to retain its beauty and wood protection.
Wood is hygroscopic, i.e. it can exude or absorb humidity. The exudation or absorption happens if a gradient exists between the humidity content of the wood and that of the surrounding air. In this way the volume and form of the wood can change. It may shrink and shorten or swell and expand.
This is the reason why extreme climatic conditions (particularly dryness or abrupt changes of air humidity and temperature)very quickly lead to deformations and cracks. Warm air can hold much more water (in form of invisible water vapour) than cold. Therefore danger threatens in winter by dry heated air, in areas with air conditioning, during strong exposure of the sun or near strong heat sources (e.g. heating elements).
But very high air humidity (over 75 % relative humidity) can also impair the static condition and thus the sound and durability of the guitar.
- The relative air humidity can be observed with a hygrometer, and at values under 40 % water should be evaporated, e.g. by wet towels which are put over radiators, or air humidifying devices.
- Special humidifiers can be placed inside the guitar cases or even inside the guitar.
- To counter very high air humidity dehumidifying devices may be used.