Historical Painting Techniques, Materials, and Studio Practice

Fortunately, the spirit of the eighteenth century in Britain fired a great enthusiasm
for publications on technical matters, including the materials and
techniques of oil painting. Thus, we find a rich source of information in the
various treatises, manuals, and handbooks that continued to be published into
the nineteenth century. The following will be a discussion of the kind of
information these documentary sources can provide and how this information
can influence our interpretation of cross sections and analytical results as well
as fu rther our understanding of painters' techniques.
The painter's environment
The anonymous eighteenth-century author quoted previously placed great
faith in "facts judiciously arranged, and published from time to time as they
accumulate." Yet, however important a discrete piece of information, such as
the date of introduction of a new pigment, may be in the study of painters'
instruction books, it is not always this information that provides insight into
the painter's choice of materials. Sometimes it is the tangential information
about the experience of living at a given time that provides a context fo r
what we observe now.
In cross sections of paint, the build-up of dirt between layers of paint must
be interpreted in relation to past conditions for lighting and heating. We
cannot, based on our present-day experience, extrapolate from the thickness
of a dirt layer the length of time between episodes of painting. Here, those
who study the history of technology and of domestic life are of great help.
In one source on the history of domestic environments, we find that even as
early as 1700 the use of coal fo r heating in London resulted in a "Tartanous
Smoak" that sullied the environment both indoors and out: "All sorts of
Hangings, especially the Tapestry, are in a few Years totally defil'd by it ..."(4).
Because painters who fo llowed the technique of "painting in stages" were
obliged to wait between applications of paint for the underlayers to dry, a
fairly rapid build-up of dirt could be expected under the conditions described,
far more than our late twentieth-century environments would convey.
The level of air pollution in the days of coal heating also caused great concern
among artists and their chemist advisors with regard to the role of lead in
paintings. It was thought that the high levels of sulfur in the air caused reactions
with lead-white pigment and with lead-treated oil, resulting in an
overall darkening of these materials due to the reaction product, lead sulfide.
Various solutions to this problem, including the application of nonreactive
zinc white over lead-white underlayers, were recommended. This advice to
apply zinc white over lead white was given not only for paint layers, but fo r
grounds as well; it was believed that a lead-white ground preparation could
also be subject to darkening. Cross sections taken from a painting in which
this advice had been followed show layers of two different white paints, the
presence of which would not be immediately obvious without the knowledge
of the remedial steps taken to obviate the so-called lead-sulfide darkening (5).
Aside from the dirt and soot from coal heat and tallow candles, interior
environments were also substantially colder in the winter months. In the
absence of central heating, painters found that their colors dried significantly
more slowly during the winter months, hence the advice to add materials
that hasten drying at this time of year (see below) .
Beliefs influencing artists' practices
Artists' practices were also influenced by views and beliefs that are foreign to
our era. Conservators have discovered empirically that it was not uncommon
for nineteenth-century painters to use similar varnishes in the paint medium
to those used as a final varnish. In the literature, painters were quite explicit;
they believed that using the same resin in the medium as in the final varnish
would, by ensuring homogeneity of materials, reduce the likelihood of cracking
(6). In a pharmaceutical dictionary and recipe book published in 1764,
2
Historical Painting Techniques, Materials, and Studio Practice