Removal of overpaint

Progressive cleaning

A large part of the damages found on old paintings today is due to the widespread use in the 1700 and 1800’s of caustic alkyls (sodium hydroxide, potassium hydroxide) or, to other substances and methodologies that permitted quick cleaning interventions. Therefore, a painting could have been badly cleaned in the past and been “well” retouched pictorially; it could have been given a thick layer of tinted varnish with the result giving the appearance of an intact – or almost intact – work. Undertaking a new cleaning treatment can lead to heavy criticism when the old damage is brought to light. On the other hand, it is neither tolerable nor ethical to hide behind the excuse of previous damage when the new cleaning itself is not well executed. Unfortunately, this situation is not infrequent.

In the preliminary phases of an intervention, the conservator-restorer tries to establish the current condition and conservation state of the object. The parts that are original and those areas that have been added later and that are visible to the naked eye are identified. We know that in the past, respect for the original areas of the work was a relative concept, while the total effect of the outcome – notwithstanding large areas of overpainting – was important. Often, the restoration intervention was not limited to only damaged areas, and large parts of the painting were covered by layers of color only because of their proximity to the lacunae under treatment. Successive pictorial interventions over vast areas or even the whole of the painting were not rare. In successive eras, these types of interventions were aimed at “updating”, “improving” or occurred as a result of changes in tastes and fashion of the owner or the art market. In addition, it should be noted that overpainting can be found in attempts to forge and falsify paintings.

Raking light and visible light

An initial evaluation on the part of the conservator-restorer is possible even without use of special diagnostic techniques (such as ultraviolet fluorescence or infrared). In terms of previous pictorial interventions, they can often be recognized due to the chromatic changes – as well as physical and superficial differences – with respect to the original. It is not unusual that even the most expert eye can not correctly evaluate the amount of previous restoration. In this case, the angle of the source of illumination can accent the differences on the surface. A light source that hits the surface at almost a parallel angle(raking light) can assist in spotting surface differences.

Antique overpaint

A restoration treatment not only serves for the consolidation and conservation of the work, but as Italian art historian Cesare Brandi stated, serves to “re-establish the original unity.” This unity can often be found by removal of the “additions”. Brandi however also poses the problem of the conservation of the added parts. From an historical point of view, these additions should be conserved because “their removal would destroy a document without being documented itself”. From an aesthetic point of view “if the addition disturbs, alters or obfuscates …or detracts in part from the viewing of the work of art” it must be removed. The conflict that Brandi puts forth can only be resolved by adequately justifying the intervention. The removal of an addition that does not disturb, alter or obfuscate, and that only brings to light the ground preparation or the support surface is not well justified.

UV fluorescence and transillumination

In order to evaluate the condition of the work – and in particular – in order to help identify previous pictorial interventions that may be covering original parts of the painting, one can use various diagnostic techniques that render the overpainting partially transparent (for example transmitted light and infra red transmitted light and x-ray radiography). Selective micro-samples can be taken, and, when studied under a microscope can assist in understanding the cross-section structure of the work. In general, one can affirm that the possibility of improving the quality of the intervention by means of today’s pictorial reintegration makes the removal of the addition usually preferable.
In many cases, therefore, the old retouchings have to be eliminated because the aesthetic qualities or original mechanics have been lost.

Overpaint removal

Once the necessity for the removal of the overpaint has been definitely established, the methods used are substantially the same as those for cleaning the pictorial surface. This includes mechanical removal.
The medium or binder of the overpainting can be quite varied. In addition, the ageing process could have provoked structural modifications changing the chemo-physical properties and rendering the overpaint practically insoluble for the majority of the solvents usually employed in cleaning. In this case the operation will be extremely delicate in that one must use solvents that will work on the binder of the overpaint without attacking the underlying original pictorial layer. Due to the fact that this layer is often more fragile than the additions, the restorer-conservator will only soften the over-layer to be removed. The removal will then be completed mechanically, under constant observation with a binocular microscope.

Manfredi Faldi – Claudio Paolini