After thirteen years, I want to finish an oil painting.

​I’m sure our conservation experts will give a more complete answer than this, but in my opinion (as a painter) the proposed approach sounds like a fairly complicated combination of materials, even more so if a transitional layer of varnish or oil is applied first. If you are determined to use this panel (instead of transferring the image to a new one), I would make sure the existing paint surface is clean, and just have at it. Any time issues with adhesion or cracking may be a factor, it’s advisable to paint thinly and avoid broad, continuous impasto, because some areas may perform better than others.

One more thought: If you are just interested in the essential shapes and colors in the unfinished work, would it be out of the question to sand down some of the original paint to improve adhesion? (With personal protective gear and appropriate cleanup, obviously)

Hi Cristian
I am glad that you took the time to post here.
It is true that many advise against applying paint to works that have dried for an extended period of time. I have never read of any scientific study that fully explains and proves this contention, but it does seem to have some validity based on empirical evidence. Additionally, as a painting conservator who has conserved many works that were overpainted in oil paint, it is common to find poor adhesion between the original paint and the much later overpaint. The reasons for this are likely quite complex including surface grime and old oxidized varnish residue between the two campaigns of paint.
The second issue here is the concept of overpainting an alkyd work with oil paint. In general, it is preferable to use faster drying paints in lower layers and slower drying in upper layers. The length of time that your painting has dried sort of negates that from being an issue here even though alkyds do indeed dry quicker than most brands of oil paint. More salient is the preference to use paints that are more rigid in the lower layers and more flexible paints in the upper layers. It is also important that the painting’s surface is not so glossy and closed off as to make it difficult for any subsequent layers to adhere adequately.  Recent research seems to indicate that alkyds are more brittle than oil paint. However, most of those made for artist’s use in the past had much lower pigment load than similar oil paints and result in a rather glossy surface and may effect adhesion. You are also saying that you used titanium white for the initial layers, which creates a rather brittle paint so the situation here is very complicated, and there is no way to state definitively that a specific formula will produce the desired results. Your use of additional oil and varnish probably further complicates this. To have a hope for success, you will likely have to “finish” this work with relatively few additional layers and all subsequent oil paint layers should have a bit of additional oil added to conform to the flexibility principle.  You may end up with a perfectly stable work. However, it is certainly possible that you efforts could be in vain. If your initial composition was painted using rather fat layers or with substantial amounts of additional medium, you are probably much better off just starting the composition anew.
As a general rule, though, I am not saying that one cannot return to a painting years later as long as a number of criteria are observed. First, the original painting should not have layers of fatty glazes or medium rich applications, which would cause mechanical adhesion issues. Secondly, one should abrade the surface in some manner to create a mechanical tooth to which the subsequent oil paint layers can adequately adhere. I do not mean sanding away the painting, but using an abrasive (eg 320 sandpaper) to remove any skin of drying oil from the surface before resuming painting. I would then wipe the surface with an aromatic containing mineral spirits or even true turpentine to degrease the surface. Finally, and only if you are going to repaint the whole surface, I would probably oil out to promote adhesion with the subsequent layers. PLEASE READ OUR PDF ON THE USE OF OILING OUT, IN OUR RESOURSES SECTION, BEFORE PERFORMING THIS STEP.
I am sure that others will have a different take on this subject but that is mine.
Brian  

Brian, Some time ago, one of the paint chemists working for Utrecht suggested a remedy for beading and resistance on oil-primed canvas: wiping with household ammonia to remove oil glaze from the surface. Does this make sense​ at all? Would it be of use when resuming work on an older painting?

​Hi Matthew

There is a certain amount of logic to the concept. The high alkalinity would certainly saponify and/or disrupt the oily residue at the surface. It would also likely destroy the uppermost oil matrix making it overly friable and desiccated. In practice, the results would probably vary from perfectly fine to complete interlayer delamination. This is not a practice that I would condone.  

Thanks, Brian- that makes sense. It’s gratifying to have this cleared up!​

​Cristian.
I have slightly amended my post as a few of my stements were not well worded and even contained a factual error. None of this changes my overal suggestions to you but it is improtant to make sure that MITRA uses the most up-to-date information.