Question asked 2017-11-06 14:54:53 ...
Most recent comment 2017-11-07 20:05:12
Could you please talk a little about the practice of using isolating varnishes between layers of paint?
Personally I don't do it, but some advocate it so it would be good to have some authoritive documentation to refer to.
Answers and Comments
I will assume that you are talking about the use of
isolation varnishes between layers of oil paint. Isolation varnishes between
disparate paint systems are a different idea and may or may not be advisable
(eg applying a coating over a very absorbent aqueous paint system to cut the
absorbency before applying oil glazes) Also, the concept is different with some
other mediums. I can see no really issue with using clear interlayers of
acrylic dispersion mediums between layers of acrylic paint. Acrylic dispersion
are an excellent adhesive, where drying oils really are not.
This use of isolation varnishes in oil painting should be
discouraged for a number of reasons. First, it is generally a bad idea to
reduce the mechanical tooth of a paint layer, which could promote delamination or
flaking of the superimposed layer.
Second, adding the varnish layer between paint layers will
introduce an unnecessary solubility issue. Even if it is covered by additional oil layers, the varnish could be attacked and undercut during a restoration campaign resulting in the loss of all subsequent layers. For instance, a layer of natural
resin between paint layers will create a paint stratigraphy that is sensitive to hydrocarbon solvents, even those containing a low proportion of
aromatics. A layer of shellac between oil paint layers introduces a sensitivity
to alcohols, etc.
Additionally, the use of varnish interlayers creates a
more complicated paint stratigraphy. We know from examination of historical paintings
that the more complicated the stratigraphy, the more likely there will be some
failure in the future. This does not mean that one has to create paintings in
only a few layers, but you should aim to use as few layers as is necessary to
create the desired effect.
The varnish interlayer will also respond in a different
manner to movement of the substrate than will the paint layers below and above
it. It will also age differently. The flexibility of the varnish may change drastically over time making it less flexible than the layers that it is covering. Etc, etc. So, for the above reasons, and likely many
that I am not thinking of at the moment, it is really best to avoid the use of isolating
varnishes in oil painting.
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