Boulle marquetry, named after Andre Charles Boulle (of German parents but active in France during the late seventeenth and early eighteenth centuries), is made from brass and turtle shell. It is cut from a ‘packet’ comprising two sheets of brass interleaved with two sheets of turtle shell and taped together with a paper pattern of the design on top. Many hours of sawing the shapes using a fine bladed fretsaw are involved to produce the marquetry panels. The ‘waste’ brass from one sheet is removed and replaced by the turtle shell pieces which exactly match the shape of the apertures formed. The ‘waste’ brass from the first sheet is then combined with the corresponding shell ‘waste’ from the second sheet of turtle shell. Thus from one ‘packet’ of two brass and two turtle shell sheets two marquetry panels are created, one with turtle shell inlaid within a brass ground and the other with brass inlaid within a shell ground. These are known as ‘premiere partie’ and ‘contra partie’ respectively. Thus after many hours of cutting and subsequent assembly two pieces of boulle furniture were produced, the ‘contra partie’ version being less popular and usually selling for less than the ‘premiere partie’ example. In the ‘premiere partie’ example of this article it can be seen that the turtle shell appears to be red in colour. This is because it is mounted on red pigmented paper which is visible through the translucent turtle shell. In the nineteenth century additional colours were used as a background and I have seen examples where green and blue pigments have been used instead of red.
And so to the title of this article, what is the ‘trouble with Boulle work’? From the outset it is very difficult to glue brass to timber. The workshop diaries of Andre Charles Boulle refer to examples of his work being returned within a matter of only months because the brass had become unstuck. During preparation the back of the brass would be scored to provide a ‘key’ for the glue, and then cleaned and rubbed with Garlic to aid adhesion before the glue was applied. The French found that the best glue for the purpose was fish glue made from the swim bladder of the sturgeon fish. Today it is not uncommon to find that brass has become loose and is either missing or has become torn or bent. Similarly the turtle shell may have become loose and may even have been lost. Aside from the deterioration of the adhesive the shrinkage of the timber substrate is a further cause of the lifting, damage to, and loss of brass and turtle shell. This shrinkage of the timber substrate may also mean that some pieces of brass have to be trimmed to fit the now smaller aperture.
In the example in question some brass inlay had lifted and become distorted through being caught by clothing and dusting etc. There were some small pieces of turtle shell missing and many that had become loose. Fortunately all the pieces of brass were present. I say ‘fortunately’ because cutting brass marquetry is a thoroughly tedious task in which the very fine jewellers saw blades seem to break with alarming frequency. Consequently I tend to refer pieces that require a lot of replacement brass cutting to a specialist Boulle practitioner!
A number of pieces of damaged brass were removed and then carefully hammered flat using the appropriate tools. One piece had to be shortened by around 0.5mm using a file. The remains of the original glue was softened and removed from the back of the brass and from the mating aperture on the cabinet. As per the historic practise the back of the brass was rubbed with a cut garlic clove and fish glue applied before the piece was inserted into position and cramped into place.
A couple of small pieces of turtle shell had been lost over time. The client asked if something could be done to blend-in the small voids rather than go to the expense of cutting new pieces of shell marquetry. The use of turtle shell is bound by the rules of the multilateral CITES treaty (Convention on International Trade in Endangered Species of Wild Flora and Fauna) which since its enforcement in 1975 bans the use of the shell of the Green turtle traditionally used in Boulle work. Unless a verifiable source of ‘antique’ shell is available, commercially available synthetic substitutes must be used. In this particular case the voids were very small (less than a thumbnail in size) and a very convincing and economical solution was achieved by mixing coloured waxes and pressing them into the voids before smoothing the surface to match.