Part 1 of this post contained historical information about Priest, an introduction to the materials from which it was made, and an assessment of its current condition. The following post will discuss the proposals for the conservation treatment of this panel.
The main concern with the Priest is its instability. The use of two somewhat incompatible materials – glass and plaster – has meant that over time, the plaster support has bowed outwards and the glass has become detached from it, which has compromised both the integral stability of the panel and also its aesthetic appearance.
The priority for the treatment of this panel is to ensure that it will not collapse any further. This will necessitate the removal of the painted backing plate, and whilst this is separate from the panel, there will be the opportunity to reinstate the pieces of glass that have fallen away from the plaster, returning the panel as close as possible to its original intended appearance.
Painted Backing Plate
The backing plate will need to be removed in order to access the glass and plaster at the back of the panel. This will mean that the panel needs to be laid on its front in a supportive cradle. Once this has been achieved, the nails and wood holding the plate in place will require documentation and then removal, and then the plate can be taken out.
The plate itself is coated with a thin layer of grease and dirt, and so this will need to be removed. It is likely that this will require a ‘wet’ clean – which will involve the use of de-ionised water and ethanol in order to cut through the grease, and this will need to be done on both sides of the glass. The paint used on the outside of the plate will have to be avoided as it has not been fired onto the glass, and so a microscope will need to be used to ensure that no liquid comes into contact with it, otherwise the pigment will dissolve.
The plate is broken into two pieces, and the use of silicone is recommended to adhere these back together. The edges of the glass will requite cleaning with acetone before any adhesive is applied, and this will need to be done very carefully to avoid the paint.
While the backing plate is away from the frame, the pieces of glass that have fallen from the plaster support can be collected, documented, cleaned, and their original positions identified. In the areas where adhesive has previously been used, the outline of the piece of glass formerly attached has left an impression in the adhesive, and this could be used to help identify which piece went where.
The glass that is still secure within the plaster can be cleaned with a soft brush to remove any dust. That which is separate from the plaster can be given a wet clean before it is reinstated, to remove any dust, dirt, and adhesive residue.
At this point it is suggested that Paraloid B72 is used to adhere the glass back onto the plaster. This is recommended as it is reversible, and though a ‘wet’ mixture, the acetone within the mixture evaporates at such a rate that it would not ‘sit’ on the surface of the plaster for long enough to cause damage.
Whilst the backing plate is separated from the panel and the back of the panel is exposed, the stability of the glass can be assessed, to ensure that no other pieces are likely to fall from their positions in future. It is not advised that the backing plate be removed more times than absolutely necessary, and so this is a good opportunity to undertake some preventative conservation.
The plaster shall undergo a ‘dry clean’, in order to remove any dust and cobwebs that have formed on the surface during the panel’s years in storage. This will involve using a soft brush, lightly dusted across the surface in order to clean it. It is referred to as a ‘dry’ clean as there is no liquid involved, and due to the nature of plaster, it is preferred that liquid is avoided unless it is necessary.
The cracks in the plaster can be consolidated with Paraloid B72 in order to stabilise the network, as this is integral to holding the glass in place. Though it would be possible to use new plaster to consolidate the cracks in the original plaster, there are numerous problems with this approach. A new batch may not adhere to the older plaster, and there is a possibility that they may separate and fall away at some point in the future. Similarly, in adhering new to old, the moisture in the new mixture would compromise the stability of the older material. As discussed above, the Paraloid B72/ acetone mix will ensure that liquid does not sit on the surface of the plaster for a prolonged period of time.
The wooden frame is generally sound, however in areas, parts of the beading has come loose and shifted its position, and some nails are missing. In this instance it would be possible to re-set this by using a new nail in the old nail-hole, and this would ensure that the frame is able to retain its stability and hold the panel in place.
The frame can be cleaned using a soft bush and a smoke sponge. The latter is a vulcanised rubber sponge that is swept gently across a surface and absorbs any dust and grime. This is to be used after a soft brush has removed any harder deposits which may otherwise scratch the wood when a smoke sponge is moved across it.
The paint is of a powdery consistency and is not solidly adhered to the glass, which may account for the area of loss. Therefore when being handled in the future, extra care must be taken, ensuring that nothing touches the plate or the paint. Though a ‘ghost’ of the paint is visible, it is not so definite that paint could be applied with confidence, and any moisture on the original cold paint would harm it, and so the painted areas of the backing paint shall be left untreated.
The removal of the exterior backing plate is necessary to reinstate the missing glass, which would include removing the nails, wood and plaster holding it in place, and manoeuvring it around the black paper attached to the wooden frame. Anything taken away in order to remove this plate would be catalogued, and reinstated in the same position when the plate is put back into place.
There are some areas where the black paper used to block out the light between the panel and the frame is missing. In those areas, new black paper shall be added to the frame to maintain this function.
There is already substantial cracking of the plaster that was designed to hold the plate in place, and in some areas bits have become loose and fallen away. Therefore when these areas are put back, and after the plate is replaced, their reinforcement with Paraloid B72 will not only hold them back in their original positions but also ensure their strength into future.
To Be Continued…
Part three of this blog post will concentrate on the conservation process itself, and will guide through the decision making processes and chosen treatment methods used to conserve Priest.