Unbodied, Bodied, Blown and Boiled Oils

[George O'Hanlon]

Originally posted by rileyfl:
I noticed that some of them had undergone dramatic color changes compared to each other than when I received them. Is this expected? Will placing them in sunlight cause them to revert to their former color? The pale grinder's [Pale Grinders Linseed Oil--ed.] and v-b high viscosity [Vacuum-Bodied High Viscosity Linseed Oil--ed.] types seemed to have suffered the most change.

It is expected that vegetable drying oils darken or yellow when stored in the dark for a period of time.

Vegetable drying oils, especially those with three double bonds, yellow with aging. The yellow color bleaches significantly when exposed to light; hence, yellowing is most severe when films are stored in the dark. The reactions leading to color are complex and are not fully understood. Yellowing has been shown to result from incorporation of nitrogen compounds, and is increased markedly by exposure to ammonia. It has been proposed that ammonia reacts with 1,4-diketones formed in autoxidation to yield pyrroles, which oxidize to yield highly colored products (Robey, 1962).

A review of the cause of yellowing concludes that previous suggestions do not correspond to expectations from the mechanisms of drying of oils. Mallegol also showed that yellowing of poppy seed oil is almost as severe as that of linseed oil, yet poppy seed oil contains very few fatty acids with three double bonds. It was proposed that yellowing results from contaminants in the oils but specific contaminants were not identified (Mallegol, 2001).

I would expect Pale Grinders Linseed Oil to yellow considerably when stored in the dark, because it contains greater amounts of linolenic acid than the other oils, but this yellowing is completely reversible when exposed to even a brief period to light.

I am wondering how you compared the oils, especially the Vacuum-Bodied Linseed Oil, to make the determination that it yellowed significantly more than refined oil.

It is true, however, that bodied oils (often called "stand oil") yellow less than untreated drying oils. This is due to higher degree of polymerization of such oils.

Sources
Robey, T. L. T.; Rybicka S. M. (1962) Paint Research Standards Technical Paper 217, 13(1), p. 2.

Mallegol, J.; et al. (2001) Studies in Conservation, 46, p. 121.

[rileyfl]

Not to be picky, however, I would not have used the word "significant" or any derivation to describe the change. As a retired research scientist, that term has a specific working definition to me. My comparisons were based on the NP oils at the time of purchase and their relative color compared to a glass bottle of refined oil made by a different company. The initial color differences among the NP oils at purchase were what one would expect from the technical specifications given for them by NP (the v-b was very light compared to epoxide, etc). And, I jotted down my visual comparisons between the NP types and the bottle of the other brand. The "other brand" container was on a bookshelf where it had been for several months.

George, my comments do not constitute a valid test, but are simply singular observations. I made no measurements with equipment to document color changes. But, the v-b high viscosity is much more yellow than the pale grinder's (and the other brand) after a few months in the dark. This result, in addition to the markedly minor change in the aged, refined oil color, were the reasons why I posted the information. I would have surmised that both the refined and pale grinder's would have yellowed more than the v-b but these changes did not happen. More curiosity than anything else. I have no concerns about any negative impact on a painting for any of these oils. Just a relatively new painter who is curious about the technical side of the process (likely an outlet from my past career).

[delsarto]

rileyfl, maybe it was because you used the words, "dramatic" and "considerable" in describing the supposed changes. I can see how those words might be considered similar to the word, "significant". I certainly got the impression from what you wrote, that the supposed changes were "significant". Also, as a former research scientist, you are certainly aware that making these claims without proper testing makes the claims unreliable. I am surprised, considering your former occupation, that you would even make the claims at all. Not trying to be rough on you, but how does anyone really know what really happened? But, I will say, that if anyone read your initial claim, they might simply believe it, without any proof. They shouldn't simply believe it, and as a former scientist, you would certainly agree with that. But, people could get false information, or inaccurate information, if they simply believed everything they read. You understand, I'm sure. Again, not trying to be rough on you, but you could be "blowin' smoke" about this whole thing, or you could be absolutely genuine but inaccurate, or you could be both genuine and accurate. It's making the claim in a public forum that concerns me. Anyway, that's my 2 cents on it. [img]smile.gif[/img]

[ 10. January 2011, 08:19: Message edited by: delsarto ]

[George O'Hanlon]

Originally posted by rileyfl:
I have no concerns about any negative impact on a painting for any of these oils.

Presently, the yellowing of vegetable drying oils in the darkness is not well understood, and as I cited in my previous post, the expected mechanisms that give rise to yellowing in aging films do not always do the expected. However, studies have shown that yellowing in the darkness is reversible (Levison, 1985).

Source
Henry W. Levison (1985) "Yellowing and Bleaching of Paint Films", Journal of the American Institute for Conservation, Vol. 24, No. 2, Article 2, pp. 69-76.

[rileyfl]

Two things:1) The term "significant" ( including derivatives) has a specific definition in the physical and biological sciences. I spent my life using that word in that environment, therefore, the reference to my use of the term was surprising to me. But, it's not a biggie; just clarifying; and 2) My "claims" are unreliable? And, your evidence for that conclusion are my "claims" and how they were generated, except you aren't sure you can believe what I wrote? You are a funny guy. I was posting personal observations on this forum to ask a question, but, not making any claims about NP products or any other brand. I was surprised by the v-b oil darkening more than the PG or refined oils and wondered if someone else had an answer.

I was not making any negative claims about NP products. You seem to be somewhat defensive of NP based on your reply here and also at times with others in previous posts. If I had a problem with a purchase from NP, I would contact them in the appropriate manner in order to resolve the matter. And, I have not had a problem with any item I have purchased from NP.

Now, as far as asking a question in a public forum......Give me a break.

Thanks, George. I am familiar with the material you posted. I was just curious if you had any idea about the differential response I observed. I'm confident that all the oil types will lighten up over the next few weeks.

[George O'Hanlon]

Originally posted by rileyfl:
I am familiar with the material you posted. I was just curious if you had any idea about the differential response I observed.

Unfortunately, we do not have a clue as to why there is a difference in the observed yellowing after storage in darkness that you observed for these types of oils. We have observed that the bodied oils yellow less upon aging, but we have seen that the Aged, Refined Linseed Oil yellows very little after being stored in darkness and upon aging. This is the oil we predominately use to grind Rublev Colours Artists Oils.

[delsarto]

rileyfl, you are relatively new to painting, as you already explained. You first described the supposed changes as "dramatic" and "considerable". Then you got "picky", (your words), about the word,"significant". Now, you object to me stating basically, -that just because you claim there was "dramatic" darkening, I am wary of such a claim that flies in the face of extensive and common knowledge among painters and paint makers. Really, must I accept whatever you say? Of course not. Just as you are free to reject my words. Be well. [img]smile.gif[/img]

[rileyfl]

I'm not sure why one would expect an average person to detect color changes that are not obvious to experienced painters. I would expect the opposite. I simply stated that your opinion about my use of adjectives had no basis; you simply chose to conclude that I am not describing the color changes accurately; you offered no basis for your conclusion other than I must be incorrect in my use of terms. Of course, you defend your opinion by suggesting that my lack of painting experience somehow affected my ability to differentiate colors and my opinion was less than useful in comparison to your's which is based on your vast knowledge and experience. However, I have no idea what your background is and , frankly, could not care less.

Why do you get so offended and take everything so personal? In this type of forum, all you have to access a posting is what was posted.

Since you are wary of my terminology, I will attempt to upload a jpeg with the 4 NP oils. As already stated,these oils seemed to fit the descriptions George lists in the tech specs for them (V-B HV was the lightest color; I could not discern any difference between Refined and PG, however, both of these were darker than V-B HV; and Epoxide was clearly a darker color). After a few months in a drawer, you have the oils as shown. These were all handled the same after reciept (unpackaged; evaluated for color differences; and then placed in the same drawer). Again, I was not surprised by the yellowing of the oils, but by the differential reaction among them.
I'm not sure how many years one would have to spend painting to realize that linseed oil darkens after extended time in the dark. So, I guess we would be in agreement on that.

However, I did not expect the V-B HV oil to darken more than the others. Perhaps this is common knowledge to you and others with years and years of experience. If so, then please explain why the V-B HV darkened more than simple refined oil. Or, so much more than PG oil? This did baffle me and to date you have not explained this result but simply stated that you did not believe what I posted. I feel like I'm debating with a 5 year-old.

Hopefully the jpeg will make it through the net. The photo is of the 4 NP oils and was taken under the same conditions in terms of light, etc. No, I would not have submitted this image if I were sending an manuscript to a scientific journal but would have used a copy stand, etc. If you believe the conditions of the photo somehow altered the color of the oils, I would certainly make the needed changes and resubmit a photo.

Maybe folks could guess which of the oils is which. I purchased the Refined, Pale Grinder;s, V-B HV, and Epoxide. The Epoxide should be easy to pick out. [img] c:\art\4npoils.jpeg [/img]

[rileyfl]

OK, the image did not go through so let me figure this out and I'll send it. Any help would be appreciated on uploading.

[delsarto]

Originally posted by rileyfl:

Why do you get so offended and take everything so personal?
[img] c:\art\4npoils.jpeg [/img]

I actually did not take anything personally, nor am I offended. We are simply two different people with different experiences and opinions. So for me, I am ending my part in discussion with you concerning this, and wish you the best. [img]smile.gif[/img]