rheology of painting for glazingApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2019-11-30 20:46:58 ...
Most recent comment 2019-12-02 12:40:11
I always see people watering down there paints when they are going to make a glaze. Many books talk about avoiding this bc if one goes extremely past the CPVC this will create an unstable film. Is there a way to guage the making of paint for a glazing technique? Is there some sort of general rule or rule of thumb that one should take into account when mixing paint for a glazing technique?
Answers and Comments
While some oil colors have enough oil to reduce simply with solvent, most will be reduced too much to retain the critical optical function of oil in the glaze. Generally, application of paint in thin "washes" with solvent alone tend to settle in a dull, lackluster layer that is weakly bound and lacks optical clarity. Viscosity is important in glazing, because the consistency must preserve pigment suspension, but also allow manipulation and removal while wet. A small amount of bodied oil (stand oil or sun-thickened linseed) to the medium lends this property, but too much makes the paint sticky and difficult to distribute and wipe away. A good glazing medium should also have enough tack to prevent beading. Composition of the underpainting is important here too- colors need to be resistant enough to wipe clean, if necessary and to resist staining from subsequent layers.
One method of preparing glazes from
modern commercially-prepared oil paint is to add low-refractive index
white pigment—commonly referred to as "extender pigments"
or "fillers"—to the paint. While this increases the
pigment volume concentration (PVC) of paint, a small amount of oil
may be added to maintain the paint near its critical pigment volume
concentration (CPVC). Pigments of low-refractive index, i.e., chalk,
silica, kaolinite, etc., do not absorb or scatter light as do color
pigments or high-refractive index white pigments, and hence appear
translucent in oil paint. These were commonly used to extend paint by
the old masters and can be used to create glazing tints with color
pigments. Extender pigments also alter the rheology of paint to
provide interesting behavior in their flow and brushing properties.
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