Adhesive properties of sun thickened oilApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2018-10-18 17:09:14 ...
Most recent comment 2018-10-22 17:37:04
Ralph Mayer speculates that, because sun thickened oil is partly oxidised, it's adhesive proberties may be compromised to some extent.
Do you know if this has been tested at all?
Answers and Comments
My guess is that if this has been studied, it was by the
industrial/household paint manufacturers in the early 20th century
when these materials were still common in industry. I will take a look at a few
old manuals to see if I can find anything. Perhaps sone of our moderators
working in the art materials industry know of such a study. As to the basic
concept, it is in line with what we believe about drying and adhesion. The
greatest adhesion would likely take place when a drying oil goes through its
whole drying curve without being disturbed. This is the technical answer. Sun
thickened oil behaves differently in actual practice. In most circumstances, it
would be used in excess of the minimum for adhesion: painting and glazing
mediums, etc. It should retain all the adhesiveness necessary for most uses. Whether
it is the best choice for a given duty is another matter. It is sufficiently
different in handling from stand oil and other thin and bodied oils making it
another tool in the kit.
One of the problems here is that sun thickened linseed oil is such a laborious process and so archaic that it was probably never used in industry (the people that are most likely to have performed serious, repeatable, scientific testing).
The references that I have consulted speak about the film strength of blown and oxidized oils (the closest analog that I can find), stating that those that are short, more oxidized, and perform poorer in the long run than those that are longer, and less oxidized. This comes from Chemistry and Technology of Paints by Toch. He also references ASTM standards but again, these are unlikely to have been performed on such a labor intensive, wasteful, expensive, and unwieldy process as sun-thickening.
There are likely less rigorous tests performed by artists and or perhaps inhouse tests by some art material manufacturers but I do not have access to these if they exist. Maybe others on this forum do.
To make a rigorous and valid test I believe that one would
need to start with linseed oil of a known composition, acid number, etc. and
then subject samples of it to the various refining, bleaching, and thickening
processes. Thicker samples would need to be thinned to create a uniform film thickness (complicated in itself). They would then need to be applied as a clear coating and
pigmented with a standardized mixture of pigments. Drying times would need to
be calculated. Finally the resultant films would need to be subjected to the
various tests used to determine “film strength” (mechanical, chemical, etc) You
can see how difficult this would be, especially as the materials have little
industrial application today.
Some of the complications regarding film strength
are mentioned in this thread:
This Page Last Modified On: