Wood

Generally speaking wood has been used in the past for both structure and decorative purposes. As wood for structure, in the Western hemisphere, both pines and/or oaks were used. For surface and decorative purposes a wide "palette" of woods has been chosen: ebony, palissander, kingwood, rosewood, calamanderwood, boxwood, tulipwood, sycamore, maple, walnut, mahogany, satinwood, elm, and many more.  In restoration one of the following three criterions is and has been applied to the election of woods in the moment of replacing wood or completing a lack of material:  Replacing or completing with the exact species of wood, and retouching it in order to imitate exactly the original material.  Replacing or completing with the exact species of wood, leaving some differences in color and leaving the matching of edges between the new material and the old one visible, making the restoration noticeable at close range.  Replacing or completing with a different kind of wood and matching color, degree of brightness of the finishing, etc., with or without matching edges, with the same intention as above.  I personally prefer the second option and even the third. My general criterion favours the aesthetic integration of the object, while allowing the easy recognition of the restoration process (it is also recorded in my final reports to the client). The result is an object that can be looked at without the eye being catched by the deteriorated or lacking parts, keeping it recognizable in its age and history.

Finishings

Surface finishings have changed drastically in the present century. However regarding "antique" furniture we must think about three kinds of materials:  Varnishes based in shellac.  Varnishes based in copal resin. .

Wax

Wax.   The first kind are finishings that are more or less based in a resin called shellac, product of the secretions of an hemipter insect called Coccus Laca, from the south of Asia, specially India.  There are several kinds of shellac, mostly as a result of its processing. Presently the most common is the orange colored, sold in thin and little scales. It is dissolved in ethanol or methanol indistinctly. The most commonly used is methanol, but not necessarily the best procedure.. A rule of thumb in the preparation is to put a certain amount of shellac in a glass flask and then alcohol so as to cover it and "a little more". The solution must have a viscosity between water and milk to begin the process called "French polishing". This is a method of applying the shellac by means of a small piece of cotton wrapped in a thin, dust- free, non- fibrous cotton fabric.  The solution is poured in a little amount at a time in the inside of the cotton and applied over the wood by means of a circular, non-stopping motion and a progressively more diluted solution, with the aggregate of little "touches" of pumice stone in powder as a filler of wood and vaseline as lubricant. The dilution and continuous rubbing has the effect of flattening the surface and giving, in the final steps when only alcohol is used, an incredible shine, impossible to obtain with other methods.  Shellac has also reflecting and absolutely different tactile properties from other kinds of finishings. Shellac, at least when new, is identifiable without doubt:: something between oily-glass and silky.  Conservation and restoration of this finishing presents many problems as shellac is extremely sensitive to water and alcohol (drinks and beverages). Therefore, valuable furniture with this kind of surface must not be used in daily living or similar situation. Being properly used, shellac finishing doesn't need special care, apart from being dusted and, in certain objects, carefully and conservatively rubbed with a microcristalline wax, and avoiding direct exposure to sun light.  The restoration of shellac can be performed in two ways: its complete removal and remaking when deterioration is so extensive that seriously compromises the aesthetic carachteristics of the wood under it, or a careful cleaning and partial "remaking" of the finishing. The first process must be considered carefully taking into account the risk of destruction of deliberate staining or shading andor natural darkening and other changes in the wood.  It is strongly advised that this procedure (the complete removal) be made by an expert restorer and with methods that preserve the changes suffered by the object along its history (if they don't seriously compromise its aesthetic unity).  Another important substance in finishings of antique furniture is hard resin varnish. As there are several kinds I will only mention the one that is made of copal resin, linseed oil and essence or oil of turpentine (or plainly turpentine). Copal is a hard resin obtained from different species of trees; linseed oil is extracted from the seeds of the flax plant, Linum usitatissimum and turpentine is a product of the steam distillation of oleoresins exuded from various conifers. The varnish prepared with these materials is hard, sparkling and with a little orange hue. When old, it becomes darker and pulverulent, due to its oxidation (oxigen absorption from the air).  The restoration process in this case is different from shellac. Copal varnish can be removed partially with organic solvents, in order to thin it and make it more transparent. Then, it must be covered with a similar varnish, conservatively, or best with a synthetic and easily removable resin.  Of course it can be removed completely with the same procedure but there are risks similar to shellac.  Wax is mainly a combination of different natural and artificial waxes: beeswax, carnauba, microcristalline and others. For the purpose of this document I will only describe beeswax, which has been the traditional compound use in protecting wood and even finishings. Beeswax is a solid material with which the bees( Apis mellifica) build their beehive and is obtained as a subproduct of the processing of honey. The wax used for furniture and wood in general is a combination of beeswax and turpentine or synthetic organic solvents in a proportion so as to obtain a semisolid paste with which to rub wood after sanding (in plain wood) or carving. It is applied in small quantities and rubbed strongly to penetrate the wood, being left to dry and repeating the operation two or three times, depending on the absorption of wood. After this step, wood is rubbed again with a clean cotton or wool fabric to acquire a lustrous shine. Wax is not a good preserving agent due to its extreme sensitivity to water, humidity and greases, but gives wood a particular shine not obtained with other methods. In fact, there is a method in which two or three layers of shellac varnish are applied to wood and then it is waxed, acquiring a peculiar semi lustrous shine. Wax is easily removed -partially or totally- by means of a combination of water and ammonia and, less dangerous to wood beneath, organic solvents. Sometimes it is necessary to remove partially the layer of wax as in the case of varnishes. The progressive darkening of the finishing ,in the case of wax, is due to the absorption of dust and different kinds of materials present in the places it was kept, originating the "patina" which, in many cases gives the object the aesthetic appearence of the its age. Obviously, extreme care must be taken in the removal of the "patina" and must be done only if the extreme darkening affects the aesthetical appearence of the wood beneath. 

Bronze

Bronze and brass are general names applied to alloys of copper with another metals (zinc, lead, tin, nickel, aluminum, etc.). Applied ornaments, handles and marquetry (Boulle work) are made of them. In high quality furniture the bronze ornaments were gilded and known as "ormolu". The classical process of making it was to apply an alloy of gold and quicksilver and then heating the ornament. This was an extremely poisonous process. Surviving pieces of XVIII century show remains of this extraordinary effective process, which must be preserved at any price. The methods of preserving and restoring bronze ornaments may consist in: cleaning with water and ammonia (very little, it's extremely pungent) and/or organic solvents to remove dirt; polishing with a mechanical device with a paste of aluminum oxide, not touching the gilded areas to bring back some of the original shine, and finally covering the bronze ornament with one or more layers of an acrilic varnish so as to preserve from oxidizing. This is made in order to restore to a certain point the aesthetic unity of the piece. Lost ornaments may be replaced with replicas made in cast fusible alloys or cast bronze (I don't agree with the last, they may not be distinguished from the originals)..