Upload new images. The image library for this site will open in a new window.
Upload new documents. The document library for this site will open in a new window.
Show web part zones on the page. Web parts can be added to display dynamic content such as calendars or photo galleries.
Choose between different arrangements of page sections. Page layouts can be changed even after content has been added.
Open the Navigation Management window, which can be used to view the full current branch of the menu tree, and edit it.
Move this whole section down, swapping places with the section below it.
Check for and fix problems in the body text. Text pasted in from other sources may contain malformed HTML which the code cleaner will remove.
Accordion feature turned off, click to turn on.
Accordion featurd turned on, click to turn off.
Change the way the image is cropped for this page layout.
Cycle through size options for this image or video.
Align the media panel to the right/left in this section.
Open the image pane in this body section. Click in the image pane to select an image from the image library.
Open the video pane in this body section. Click in the video pane to embed a video. Click ? for step-by-step instructions.
Remove the image from the media panel. This does not delete the image from the library.
Remove the video from the media panel.
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?
Move this whole section up, swapping places with the section above it.
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:
Thanks Brian, that's pretty much what I expected.So as I see it, the take away summary would be, sun thickened oil should have lost some of it's adhesive properties in theory, but this would likely be insignificant in practice.Especially considering that the oil, as a medium, should be only a small percentage of the paint film.Ron Francis
PS. I believe sun thickened oil was widely used in the Renaissance, so if there was a problem with it, I would expect it may be showing up in the conservation area.Then again, I;m not sure how anyone could tell sun thickened oil was used unless it was documented by the artist.Thanks again, much appreciated.