Applications in Conservation
The three most important forms of applications are1) Protective or Blocking Sealing of Surfaces
The temporary protective sealing of sensitive surfaces has been used in the conservation of panel paintings, paintings on canvas, wall paintings, stone objects as well as for brickwork and concrete.To seal a surface we have the choice of two methods.
Sealing off by using a spray can and from a melt (see conservation of buildings)
Sealing off from a solution leads to very unsatisfying results only. This is because of the sucking characteristic of porous surfaces which makes it necessary to apply the solution a couple of times to get an effective seal. It is only recommendable in certain situations.
The way you can work with a melt decisively depends on the melting point of the used material. To get a relatively smooth film by using a brush at room temperature is possible with material whose melting point is below 40°C. If it is higher, the melt solidifies too fast in the brush and on the surfaces, resulting in a very uneven spread of the material.
Protection of water-sensitive surfaces during cleaning
When using a soap solution (sud) to clean a surface, the edges of the surface touching highly sensitive gold-plating very often are a very critical zone. A temporary sealing of these zones with a menthol melt resulted in very good effects.
When taking off the varnish of a painting the solved resin very often penetrates through the craquelée into the canvas. You can watch this phenomenon very often on the back of paintings. This leads to a brittleness of the canvas.
If the painting allows a treatment with a hot-air gun from the backside and only highly polar solvents are used, the back of the painting may be secured by temporarily sealing it with CCD.
CCD, depending on the thickness of the canvas, is applied in one or two layers by using a spray can. To melt it a minimum temperature of 60°C is used.
8t th century
wallpainting in Steinbach basilicaThe task was the conservation of a carolingian building, here in the apsis the wall paintings were covered with a dense and quite dirty layer of sintered gipsum.
The mortar supporting the painting showed severe damage on the surface. Along hairline cracks and at the edges of mechanical damages the binding character of the mortar had diminished, the edges had become sandy and crumbled off.
Due to this a net of missing areas with sandy surfaces had developed.
The mechanism of the damage is caused by the different permeability of the surfaces.
The climatic conditions in this open room are determined by quick changes of air. This results in dew on the surface of the mortar, especially in spring.
The water is equally consumed across all of the surface, but exits mainly via the cracks and other surface damages. The fastened drying off of these areas leads to a higher level of solved salt. Although the percentage of building-damaging salt in the mortar concerned is rather low, it seems enough to make it brittle.
The combination of two actions should counter this process:
First the rather thick crust of sinter on top of the painting should be reduced. Then the existing damages on the surface should be sealed, so that the characteristics of the surface are more or less the same all over, as far as the permeability is concerned.
Taking off the crust especially is a strain on the corner zones of the mortar. Therefore the missing areas were filled with putty first.
The extremely dense net of cracks and damages asked for extreme cautiousness.
Any dirt along the edges had to be avoided. Therefore they were to be secured by temporary sealing. First tests with CCD showed, that it was not possible to achieve the necessary thinness of the film. The actual film should not put the level of the edges any higher, otherwise the level of the repaired area would have been higher than the original surrounding.
In this case we got excellent results by using a menthol melt. The menthol was heated in a water-bath, to a temperature of about 60°C, thus being safely above the melting point of 30. The material was then applied using a hair brush. The solidification worked out in a way that the material penetrated less than one millimeter.
After the binding media had evaporated the existing chalk-fog was dusted off with a vacuum cleaner and a hair brush.
2) Temporary adding of hydrophobic features to surfaces as a protection against waterIt is when the conservation job requires to work with water on the surface of an object, but you don't want the water to penetrate, when the temporary adding of hydrophobic features onto porous surfaces is asked for. This is especially the case when you clean wall paintings and the surface of stone.
The method described here is not a complete sealing off of all pores, but only a measure to make sure that water won't penetrate for a certain amount of time. It takes just a few hours for the effect to have gone to such an extent, that it really isn't effective any more. You can have sealings much more solid from a melt, even effective against polar solvents. Applying a melt only offers an advantage, when the pores of the surfaces are that big, that they can't be closed sufficiently with a film from a solvent. But even in these cases it is an advantage to apply an even layer first, and then melt it in with a warming lamp.
It is necessary to point out again the very long time CCD takes to evaporate. Without ventilation on the surface a 1mm film from the melt takes up to 30 days. You have a similar sublimation process in the pores, so that a melted sealing of 2mm means you are looking at 7 to 8 weeks of waiting. Sealings applied any deeper didn't seem to make any sense so far.
This sublimation process has been researched and excellently been described by Mrs. Nicole Riedl. (Restauro 1998 Heft 7)
Example wall painting
During the fifties gothic wall paintings in Bad Soden-Allendorf were solidified by using a glutine glue. In the course of other conservation jobs this protein layer was to be taken off because the large amount of tension in it was very dangerous for the painting.
First tests showed that the glutine solved well in water and could be detached in most areas. However, the usage of water also led to „water edges and stains“ on the surface. Using watery injection mortar showed the same effect.
Temporarily making the mortar surface hydrophobic on the other hand showed very good cleaning results without any water stains.
The following steps were necessary to add the hydrophobic features
Cyclododecane was solved 5:6 in naphta with a boiling range of 40-60°C.
Using a brush the solvent was applied onto the mortar in several applications, each following the other rather fast.
After a drying time of about 1 hour we had a coating of CCD with varying thickness.
This coating was then removed using petroleum spirit and cotton wads (Q-tips) to dab or roll it off.
The aim of this process was to get a completely free, i.e. not sealed surface in order to allow a watery solvent to be effective. At the same time the hydrophobic layer directly under the surface of the mortar should not be damaged. The way to proceed depends of course on the type of surface. Especially on very crusty surfaces it proved useful to use a brush.
To let the layer of glutine glue soak a water- alcohol-compress was put on it. (Adding about . 0,5% tylose 30.000 to the water) After about 30 minutes the compress was taken off. After that the soaked layer could be washed off with water.
Several tests with a "Karstenschen Röhrchen" (i.e. a test tube) showed that the procedure used here effectively blocked the penetration of water into the plaster for about 2-3 hours..
In areas with hairline cracks the penetration is blocked for a few minutes only. After that, the water flows continuously.
This danger can be circumvented by elevating the level of viscosity. Adding merely 0,5% tylose 30.000 where enough, to block the water even in the critical areas.
Ahrweiler - Excavated Roman Wall Painting
The condition of the individual layers of plaster (basic, middle and coating plaster) showed different types of damage. The surface was broken up in many places. All over the area pieces of varying size of plaster were missing. All three layers of plaster had in common that they bonded badly in themselves and therefore only had little adhesive connection to the particular surface.
The first goal of the conservation process was to get the different layers of plaster to bond with each other. This was to be achieved by applying Kieselsäureester KSE silic acid (KSE).
The painted surface of the mortar was to be left untouched of course, when solidifying the finishing mortar. One reason for this was concern over the depth light. Another reason was concern over the irreversibility with which the existing layers of dirt and clay were glued to the surface of the painting. The protection of the surface was to be achieved by using CCD.
To prevent that the KSE penetrates into the layers of the painting from the backside, a thick film of melt was to penetrate for about one millimeter of the paint. The working process was as follows:
Preliminary treatment of the painted plaster with cyclododecane in petroleum spirit in a ratio of 2:3
Applying a melt of cyclododecane in in petroleum spirit in a ratio of 8:2. The melt was applied at a temperature of about 95°C.
After a drying period a heating lamp was used to melt.
Adding of another layer of melt of cyclododecane in in petroleum spirit (Ratio 8:2). The melt was applied at a temperature of about 95°C.
Treatment with silic acid
The solidification was carried out with silic acid. When selecting the KSE we had to make sure that the solvent didn't solve cyclododecane film. To prevent that, by migrating, the KSE separates denser gel at the surface than in deeper areas, the production of gel was accelerated. The working process was as follows:
Montema 28 (with ethanol as solvent) was thinned (1:4) with isopropanol.
To have a gel production within of 50 min. an ammonia solvent was added.
The areas were completely flooded. Three passes were possible before the production of gel started.
Finishing treatment of the surface
Due to the flooding of the complete surface with silic acid gel developed even on those areas protected by CCD. After the evaporation of the CCD-film the silic material lay on top of the painting as a gray layer, looking like Japanese paper. This coat was easily removed by blowing or using a vacuum cleaner. Under this coat the surface of the painting reappeared in the same condition like before.
3) The Temporary Solidification
The temporary solidification of fragile objects can successfully be carried out by using a melt as well as by using a solvent.The decisive factor for the working process is the aim of the solidification.
Basically the solidification of porous material is limited by the fact that these materials have to be actually penetrated, which is true for any solidification.
The only limit for the penetration of a melt is the solidification of the material when cooling down. But even the penetration capability of a solvent is limited.
"Basically the penetration of a structure is problematic, because volatile binding media as well as their solvents only have a low surface tension, due to the non-polar structure of their molecules. The higher the surface tension is, the deeper the volatile binding media can penetrate."
At the same time I must warn of forced depth solidifications. From my experience you can expect that melts which have been entered several centimeters by warming the porous material won't evaporate completely - or only after years.
On the other hand solidifications carried out with solvents sublimed comparatively fast at room temperature. For example the temporary solidification of 30mm of sand in the Xanten example had dissolved after about 6 weeks. The temporary sublimation of the examples in Bad Soden-Allendorf and Zierenberg resisted the water in the testing tube for no longer than just two hours.