B72 Retouching Gels provide a range of retouching/inpainting media of great versatility. They are suitable for work on any scale; from the fine retouching of paint losses to large scale reconstructions. B72 Retouching Gels enable the painting conservator-restorer to imitate the original technique of the artist both on old master and modern paintings. This can be achieved by choosing the right gel or mixture of gels which mimic the rheology and handling properties of painting media used on original artwork.
Depending on the specific requirements of a particular retouching situation, the properties of the medium can be varied by:
- solvents with different evaporation rates
- hardness/softness of the gel
- concentration of Paraloid B72
The Gels can be mixed with each other and with solutions of Paraloid B72 or polyvinyl acetate to provide an infinite range of properties and final effects.
The table below illustrates the typical recommended uses of B72 Retouching Gels.
The choice of gel or mixture of gels with different drying times depends on the scale and complexity of the retouching. Three solvents of different evaporation rates are used:
- Dowanol PM (propylene glycol monomethyl ether; 1-methoxy-2-propanol) fast evaporating with an evaporation rate comparable with xylene
- Dowanol PnP (propylene glycol n-propyl ether; 1-propoxy-2-propanol) slower evaporating with an evaporation rate comparable with white spirit or Shellsol 100
- Dowanol DPM (dipropylene glycol monomethyl ether; 1-(2-methoxyisopropoxy)-2-propanol) very slowly evaporating with an evaporation rate comparable with Shellsol D60. Gel with Dowanol DPM takes a very long time to dry, and so gives the feel of working with oil paint.
More information about the solvents used
As thinners one can use the solvents originally used in the gels (Methyl Proxitol from Shell is an equivalent of Dowanol PM, Methyl Diproxitol is an equivalent of Dowanol DPM) and Industrial Methylated Spirit. The addition of IMS increases the flow of the paint. The use of Shellsol 100 and xylene is not recommended.
The ten B72 Retouching Gels provide a range of media that vary in their concentration of Paraloid B72 and the hardness/softness of the gel. By mixing gels together one can adjust the properties of the retouching medium to address the specific requirements of paint handling properties and the final appearance of the dried paint.
Fast drying gels are most suitable for painting rich textures, for underpainting and for working on a small scale. For complex retouching on a small scale, which requires more time, slow drying gels can be added.
Slow drying gels are particularly suitable for painting wet-in-wet and for painting and glazing over large areas.
Very slow drying gel with Dowanol DPM has been especially developed for the painting of large scale reconstructions and for the glazing of large surfaces. It is also used as a drying retarder for mixing with other gels to facilitate wet-in-wet painting over a prolonged period of time. It should never be used for painting impastos nor for underpainting. Paint containing Very Slow - Light 10 gel should be left for a few days to dry completely before glazing and varnishing.
Some practical considerations
Because of the high viscosity of the gels special attention has to be paid to the proper dispersion of pigments in the medium. Paint containing agglomerates of pigment particles will dry with a rough surface. Such a result can be avoided by grinding pigment with gel for longer and more vigorously or by premixing pigments with a standard solution of Paraloid B72 or solvent.
Paint for heavy impastos and textures should be rich in pigment in order to avoid shrinkage and subsequent cracking during the drying process.
Light gels should not be used for painting rich, heavy textures. Having a false body made mainly of solvent they are comparable with the traditional megilp. The resulting heavy impastos will shrink, crack and be brittle.
Paint with a large proportion of pigment made with Light gels may, when dry, give a matt, slightly rough absorbent surface. It can be sealed to prevent varnish sinking and smoothed by the application of a thin layer of gel.
For multilayer painting the traditional rules of painting should be obeyed in order to achieve a stable paint that will not, over time, start to crack. Fast drying gels, rich in pigment, should be used for underpainting. The subsequent layers of paint should be applied once the previous layers are completely dry. The top layers can be painted with slower drying gels and can contain smaller proportion of pigment. The exception to this rule is wet-in-wet glazing.
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Paraloid is the trademark of Rohm & Haas; Dowanol is the trademark of The Dow Chemical Company; Shellsol and Proxitol are the trademarks of Shell Chemical Company.