Restoration

The three ceiling paintings were painted in oil on linen.

The ceiling paintings have the following dimensions:

The left-hand canvas446 x 185 cm.
The central canvas446 x 232 cm.
The right-hand canvas446 x 202 cm.

The paintings were last restored by the firm of Hesterman en Zn. in Amsterdam around 1912.

The ‘Triumph of Peace’ ceiling paintings have become very soiled over the past century and the natural resin, varnish layer has yellowed considerably. This has been very detrimental to the paintings’ visual quality.
The restoration’s emphasis is on the consolidation of the paint layer and the removal of layers of grime and yellowed varnish. Furthermore, the so-called ‘deformation in the form of a belly’ of the linen canvas, a phenomenon specific to ceiling paintings, will be corrected. The discoloured retouches and overpainting, applied during prior restorations, will be removed.

Initial findings

During the removal of the ceiling paintings it became apparent that the Bol room is ventilated via a vent located immediately above the central ceiling painting. The vent is connected to a system of ducts on the floor above. The ducts end in the Peace Palace’s tower. This means that, naturally unintentionally, the ceiling paintings have acted as filters for the ventilation of the Bol room.

The thermodynamic conditions of the Bol room have influenced the grime accumulation on the ceiling paintings. The three ceiling paintings have been severely contaminated by loose and impacted surface grime. In both cases, there is an adhesive layer of deposited aerosols. The size of the aerosols is determinative for the extent to which they have adhered to the surface and the paint layer. The openness of the paint and varnish layers also plays a role in the level of adhesion. The abovementioned, upward flow of warm air is a particularly good transporter of aerosol particulates. In the past, people were allowed to smoke in the Bol room. A mixture of aerosols will therefore be found which primarily consists of high molecular weight hydrocarbons from the nicotine.
Due to the capillary condensation, accelerated by the non-regulated or unstable environmental factors, a great deal of atmospheric grime has been attracted. This effect is exacerbated in the Bol room by the ventilation system. This has created a large accumulation of microorganisms on the backs of the canvases, which are pulled further into the linen and will subsequently be transported through the paint layer. The breaking down of the cellulose (main constituent of linen) by the microorganisms, largely sucked up by the ventilation system above, will strongly (or in an accelerated manner) decrease the elasticity and tensile strength. This reduces the function of the doubling.

The ceiling elements were doubled with a wax-resin adhesive. The deformation reveals that the canvas is very stiff. This is characteristic of wax-resin doubling. The composition depends on studio traditions or the recipes of the restorers at the time. The last restoration was carried out around 1900. The adhesive used during this period was, if we are lucky, based on beeswax-triterpenoid tree resin-turpentine. However, usually, the cheaper and very acidic rosin was used, in some cases with copaiva balsam and/or ceresin added.
The upward airflow of the unstable heat emission of the central heating has a detrimental effect on the hygroscopic state of the original linen canvas and the doubling linen. The flow of warm air causes fluctuations in the relative humidity on the front and the non-sealed back of the ceiling elements. These flows of warmth manifest themselves in the paint layer as upright paint particles.

The painting has a so-called ‘natural deformation in the form of a belly’ thanks to the way it was hung. In particular, this puts irregularly distributed weight on the sides of the ceiling painting which causes visible mechanical damage to the paint layer. In the centre of the ceiling element, where the deformation has its largest accumulated volume, a volume increase can be discerned. The mechanical damage which can already be discerned in the paint layer, partially heralds cellulose corrosion. This need not necessarily be dramatic after 100 years, but removing microorganisms and tightening the bearer is more than desirable with a view to future conservancy.

The varnish applied last, was probably based on a triterpenoid tree resin such as dammar or mastic. The varnish was applied with a brush and later smoothed out. Owing to its matt look and greasiness it cannot be ruled out that wax was added to the varnish. The varnish has changed chemically due to ‘natural ageing’. Varnish oxidises primarily due to contact with oxygen, warm air and due to damp transport. In the case of the ceiling paintings from the Bol room, this has resulted in a yellowed layer with a somewhat bluish cast to it. The ceiling paintings’ abovementioned storage conditions have clearly influenced the varnish layer’s level of oxidation. The depth of oxidation can be measured using tests in order to determine to what depth the former may/will have to be removed. This also allows the type of resin to be determined and allows checks to be carried out for irregular or unexpected additives.

Progress

In consultation with the supervisory committee it has been decided to initially complete the primary technical documentation, to study the stretcher and to remove the first layer of surface grime. A report on our findings will be released in the near future.

Text: © Milko den Leeuw – Atelier voor Restauratie & Research van Schilderijen