Q: Some of my non-varnished oil paintings that are still
drying have developed a whitish bloom on the top surface. What did I do
wrong, and what should I do now?
A: The "blooming" can be caused by a variety of conditions.
Temperature plays an important role in the drying process. Blooming
usually occurs in cold, damp conditions because moisture can get into
the film of the drying agent you mix with your paints. Have you used
damar varnish as a glazing medium on your painting? Water in the gum
turpentine, in the jar used for making the solution, or even as vapor
in the atmosphere on very humid days can cause a dried varnish film to
bloom.
Another possible cause is working in very hot conditions. Heat can
actually cook the oil and alter the curing process, causing not only
blooming but yellowing and cracking as well.
Most oil painters are not aware of oil paint's drying process.
Unlike watercolor and acrylic, which both dry by evaporation, oil dries
by oxygenation. Oil actually gains weight through its curing process.
Many pigments also have properties that act as catalysts for
oxidation. Some colors, therefore, will dry faster than other colors.
For example, burnt umber will dry faster than alizarin crimson.
Many artists know the rule of "painting lean to fat," but most
artists don't know that this rule also applies to the pigments that are
used. Colors such as ivory black and alizarin crimson should be
reserved for the final stages and should not be used during the ìleanî
stage because they take longer to cure.
Here is a short list of the oil paint absorption properties of selected pigments:
Low Oil Absorption:
flake white, zinc white, chromium oxide green, Venetian red
Medium Oil Absorption:
cadmium colors, phthalo colors, ultramarine blue, titanium white, umbers
High Absorption:
alizarin crimson, ivory black, siennas
Very High Oil Absorption:
cobalts, viridian, lamp black
To remove the bloom:
Try mixing 1/3 part mineral spirits with 2/3 part boiled linseed oil.
Mix thoroughly and rub gently onto your painting. Alcohol, if it is not
too heavy or thick, has also been known to remove oil paint problems.
--by Camille LaPointe-Lyons