With the documentation and examination of the painting now well underway, the time has approached to develop a strategy for cleaning the painting, that is, the removal of the discoloured varnish and restorer's overpaints. While every cleaning must follow the particular demands of each individual painting, the steps we will take for the Crossing of the Red Sea are typical for the treatment of many old master paintings.
Before cleaning can commence, tests will need to be carried out to ensure that it can be done with the minimum of risk. Here are some of the steps we'll take:
Tests under magnification
The first stage will involve testing of the solubility of the varnish and potentially the paint films. During an examination it usually clear what type of varnish lies on the surface and what type of paint medium has been used by the artist. With that knowledge a suitable varnish removal solution is selected and tried out on a tiny area of the surface of the painting, usually near an edge.
This is generally done with the aid of a magnifier or microscope to see how the varnish and paint respond to the cleaning solution. If problems occur the choice is clear: stop or otherwise find another an alternative cleaning mixture, or perhaps a different method of cleaning. In most cases, when the varnish and paint layers are properly understood it does not take long to arrive at a suitable method.
Small windows on different areas of the painting
Once the cleaning tests indicate that the old varnish can be safely removed, the next stage in the process will involve carrying out slightly larger tests in different passages of the painting. The aim of this part of the process is to determine how the cleaning solution works in different parts of the painting.
The surfaces of paintings are not uniform in their composition; certain traditional pigments - for instance lead white - often form stronger and more resistant paint films than others, such as vermilion red or azurite blue. Other colours might be more vulnerable because the artist may have added a resin (similar to the varnish medium) to the oil paint medium, making it potentially vulnerable.
Furthermore, some parts of the painting might contain a different paint medium altogether: In the seventeenth century it was customary for some painters to use a medium other than the usual linseed oil for specific pigments. It was not uncommon for blues to be painted with walnut or poppy oils, which were less prone to yellowing than linseed. Other painters used a glue-like medium for blues. Investigations into Poussin's materials have shown that he generally used linseed oil but did employ walnut oil for some blues and occasionally added pine resin to his paint.
For this reason, all potentially vulnerable areas of paint need to be tested. Once this has been done it will be time to commence the removal of old varnish and restorer's overpaints.
Tests under magnification
The first stage will involve testing of the solubility of the varnish and potentially the paint films. During an examination it usually clear what type of varnish lies on the surface and what type of paint medium has been used by the artist. With that knowledge a suitable varnish removal solution is selected and tried out on a tiny area of the surface of the painting, usually near an edge.
This is generally done with the aid of a magnifier or microscope to see how the varnish and paint respond to the cleaning solution. If problems occur the choice is clear: stop or otherwise find another an alternative cleaning mixture, or perhaps a different method of cleaning. In most cases, when the varnish and paint layers are properly understood it does not take long to arrive at a suitable method.
Small windows on different areas of the painting
Once the cleaning tests indicate that the old varnish can be safely removed, the next stage in the process will involve carrying out slightly larger tests in different passages of the painting. The aim of this part of the process is to determine how the cleaning solution works in different parts of the painting.
The surfaces of paintings are not uniform in their composition; certain traditional pigments - for instance lead white - often form stronger and more resistant paint films than others, such as vermilion red or azurite blue. Other colours might be more vulnerable because the artist may have added a resin (similar to the varnish medium) to the oil paint medium, making it potentially vulnerable.
Furthermore, some parts of the painting might contain a different paint medium altogether: In the seventeenth century it was customary for some painters to use a medium other than the usual linseed oil for specific pigments. It was not uncommon for blues to be painted with walnut or poppy oils, which were less prone to yellowing than linseed. Other painters used a glue-like medium for blues. Investigations into Poussin's materials have shown that he generally used linseed oil but did employ walnut oil for some blues and occasionally added pine resin to his paint.
For this reason, all potentially vulnerable areas of paint need to be tested. Once this has been done it will be time to commence the removal of old varnish and restorer's overpaints.
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