B72 Retouching Gels were developed in order to overcome the limitations of conventional retouching media. Their behaviour is more complex than of that of Newtonian fluids and cannot be described simply in terms of their viscosity but rather in terms of their rheology, which is behaviour under applied mechanical stress.
The rheology of the retouching resin solution is modified by the development of a liquid crystal phase. The lyotropic liquid crystal phase is formed by amphiphilic molecules, a building material for micelles, which become more and more organised, so giving liquid crystal phases of increased order. The hardness/softness of the gel depends on the degree of order. It is therefore possible to produce thick resin solutions with low resin concentration. The properties of a gel retouching medium can be modified by the concentration of the resin, development of the liquid crystal phase of lower or higher order and the choice of solvent. Solvents with larger molecules, which are building blocks of micelles, will produce harder gels.
The liquid crystal phase B72 Retouching Gel with the addition of fumed silica thickens faster. This is caused by the presence of silica. However, it dries slowly enough to allow the painting of impastos wet-in-wet.
Under mechanical stress the order of a liquid crystal phase is disturbed and diminished. When Gel is mixed with the pigments on the palette it becomes more fluid. After application on the painting, the paint thickens again as the micelles reorganise themselves into a more ordered structure. This allows painting and glazing wet-in-wet without the risk of paint bleeding and mixing uncontrollably, even with solutions of a low concentration of resin.
The drying behaviour and rheology of paint made with B72 Retouching Gel makes it possible to paint wet-in-wet, to paint impastos, to paint glazes wet-in-wet and to paint on a larger scale than with a simple solution of retouching resin.