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bobbybirds
03-03-2019, 06:02 PM
Hey all,

Please forgive the newbiness of this question, but can two different types of oil based paints like walnut and linseed be used together on the same painting without experiencing issues? I have some cheap linseed based paints I have been using and have started buying so kama paints which are walnut oil based and I want make sure the two oils are compatible together before using both together.

Opinions or facts?

Delofasht
03-03-2019, 06:05 PM
Yes they can be mixed, and will be fine overall. Some paint manufacturers actually mix the two oils for making their paints even.

bobbybirds
03-03-2019, 08:27 PM
Yes they can be mixed, and will be fine overall. Some paint manufacturers actually mix the two oils for making their paints even.
Good to know! Thanks.

RomanB
03-04-2019, 10:20 AM
Linseed, walnut and poppy oils could me mixed in any proportions, they'll dry without any problems. Safflower and sunflower oils could be problematic in mixtures - sometimes paints made with them liquefy or "melt" after a few years.

AnnieA
03-04-2019, 02:00 PM
Roman, could you post a link that describes the safflower/sunflower problems you mentioned. I had never heard of that. Williamsburg has fairly recently introduced a selection of oil paints ground in safflower because of it's reduced tendency to yellow. It seems unlikely that they'd use an oil that could cause "melting" after a few years.

newbiebirds, as Delo notes, paints ground in any of the typical oils used in preparing them can be mixed.

And extra points for the word, "newbiness." :D

RomanB
03-04-2019, 03:09 PM
Roman, could you post a link that describes the safflower/sunflower problems you mentioned. I had never heard of that.

Of course. I'll cite from a couple of recent articles:

1. Franken V., Heydenreich G., Jägers E., Müller W., Schulz J., Zumbühl S. (2014) Set Back the Race: Treatment Strategies for Running Oil Paint (https://link.springer.com/chapter/10.1007/978-3-319-10100-2_22). In: van den Berg K. et al. (eds) Issues in Contemporary Oil Paint. Springer, Cham

"The liquefaction of oil paint is primarily dependent on the type of oil. Case studies suggest that semi-drying oils – sunflower and safflower oil are one of the main causes of liquefaction. Since unpigmented sunflower and safflower oil may liquefy after 5 years it seems that pigments and additives have a less significant influence on this process."

2. Zumbühl S., Scherrer N.C., Müller W. (2014) Derivatisation Technique for Infrared Spectroscopy – Characterisation of Oxidative Ageing Products in Modern Oil Paint (https://link.springer.com/chapter/10.1007/978-3-319-10100-2_15). In: van den Berg K. et al. (eds) Issues in Contemporary Oil Paint. Springer, Cham

"Ageing of modern oil paint is fundamentally different to ageing of the classical paint systems. This is strongly related to the material composition of modern artist’s paints. On the one hand, the ageing process is strongly influenced by the binder composition. Modern oil paints often consist of a variable mixture of different oils in order to control the drying behaviour of the different colours. In addition to this, general regulations with respect to the quality and stability modern pigments have changed. As a result, modern oil paints exhibit a different degradation behaviour when compared to classical oil paints. There is an increasing number of incidents where such modern paints liquefied within a few years after application (in thick layers) and drying (see Boon and Franken et al. in this contribution). This phenomenon was observed both in oil paint and in binder samples applied without pigments, fillers or additives. It can thus be assumed that the process is related to the binder composition. All incidents of paint liquefaction upon ageing so far were related to a high content of sunflower and/or safflower oil."

Full article is currently available here (https://www.researchgate.net/publication/278662954_Issues_in_Contemporary_Oil_Paint).

AnnieA
03-04-2019, 04:01 PM
Hey, Roman, thanks for that. Until any contradictory studies might be published, I'm certainly going to stay away from paints bound in those oils.I'm surprised though, as I've always understood Williamsburg to be a highly reliable source of oil paints. Consequently, it makes little sense that they've come out with their line of safflower-bound oil paints just recently. Unless there's something I'm missing...I hope Sarah Sands weighs in.

RomanB
03-04-2019, 04:26 PM
Hey, Roman, thanks for that. Until any contradictory studies might be published, I'm certainly going to stay away from paints bound in those oils. I have to say I'm surprised though, as I've always understood Williamsburg to be a highly reliable source of oil paints. So it makes little sense that they've come out with their line of safflower-bound oil paints just recently. Unless there's something I'm missing...I hope Sarah Sands weighs in.

It's complicated. Safflower oil can be of different composition naturally or it can be modified chemically. We don't know what exactly Williamsburg put in their paints, maybe they have a non-problematic variety of safflower oil. But it is better to be aware.

I feel that technically oil painting consists of compromises. We had lead white which was poisonous to workers who manufactured it. Zinc white was invented in XIX century as an alternative. Now we know that zinc white makes oil paint brittle and inflexible. One hundred years ago titanium white pigment was invented as an alternative. Now we know that its photocatalytic properties deteriorate oil paint and pigments around. Partly it could be managed with coating of pigment particles, but not entirely. Have you ever seen any artist's oil paint manufacturer who mention that they use coated Titanium White pigment? I never encountered such statements.

Same story with oils. Linseed yellows the most. Walnut goes rancid too fast and its quality heavily depends on a particular place and year of harvest. Poppy oil is made of the same plant as heroin. Hemp oil is made of cannabis. Siberian Pine nut oil is produced only in Siberia, and you have to employ lots of squirrels to collect nuts from pine cones. Every solution is a compromise.

bobbybirds
03-04-2019, 08:50 PM
Lots of great info!! Thanks all!

Harold Roth
03-05-2019, 05:51 AM
Walnut goes rancid too fast and its quality heavily depends on a particular place and year of harvest.
I keep seeing this claim about rancidity, but I have not experienced it at all. I have a big bottle of Kremer walnut oil that's been sitting on the windowsill for a year and it still smells fine. Prior to that, I had a big can of the Graham walnut oil sitting on my table for a year. It too did not go rancid.

If you keep oil in the fridge, supposedly to keep it from going rancid, and you take it out and open it up before the oil inside comes to room temperature, you will get condensation from the air inside the container, and THAT will make the oil go rancid eventually. Any oil.

AnnieA
03-05-2019, 08:53 AM
I keep seeing this claim about rancidity, but I have not experienced it at all. I have a big bottle of Kremer walnut oil that's been sitting on the windowsill for a year and it still smells fine.
My understanding is the linseed smell that I particularly love because it reminds me of my mother painting and trips to "The Flemish Art Store" when I was a kid, is actually the smell of rancid oil. And that typically, painting oils may already be rancid before arriving on the art store's shelves.

This isn't meant to dispute the fact that some find linseed, or other nut oils, to have a very irritating smell.

Harold Roth
03-05-2019, 10:18 AM
My understanding is the linseed smell that I particularly love because it reminds me of my mother painting and trips to "The Flemish Art Store" when I was a kid, is actually the smell of rancid oil. And that typically, painting oils may already be rancid before arriving on the art store's shelves.
That's true, and it's exactly what I dislike about linseed oil as a medium--it smells like old, rancid oil because pretty much that's what it is. :) I'm fine with it in paints--don't really notice it--but not as a medium. Can't stand the smell of flax seeds either, much less eat them.

I use walnut oil as a medium, and if I have a bunch of paintings in my studio and it's warm weather, it can start to smell a bit of old oil from the walnut oil I use as a medium oxidizing. But it's hardly noticeable, and it's not at all noticeable when I am painting with it.

sarahsands
03-05-2019, 10:20 PM
Hey, Roman, thanks for that. Until any contradictory studies might be published, I'm certainly going to stay away from paints bound in those oils.I'm surprised though, as I've always understood Williamsburg to be a highly reliable source of oil paints. Consequently, it makes little sense that they've come out with their line of safflower-bound oil paints just recently. Unless there's something I'm missing...I hope Sarah Sands weighs in.
Hi Annie - Sorry that I am just seeing this now. I would be more than happy to chime in tomorrow. The long and short of it will be "It's complicated", but I want to help flesh out some of the issues for everyone. In the meantime, we have definitely been aware of the research Roman mentions, and have even started conducting our own tests as well as attending the conservation conferences where these topics are covered and papers delivered. Anyway, more to come.....

Gigalot
03-06-2019, 03:34 AM
=RomanBNow we know that its photocatalytic properties deteriorate oil paint and pigments around.
ПФ-115 exterior alkyd paint has 19% Talc added as anti-photocatalytic agent.
Talc addition is quite effective way to greatly reduce risk of alkyd binder photo-destruction. You can read that in Russian pigment chemistry book. :thumbsup:

Zinc in modern artists' paint have some UV light protective effect.

RomanB
03-06-2019, 05:03 AM
ПФ-115 exterior alkyd paint has 19% Talc added as anti-photocatalytic agent.
Talc addition is quite effective way to greatly reduce risk of alkyd binder photo-destruction. You can read that in Russian pigment chemistry book. :thumbsup:


It may solve problems for industrial coatings with relatively short lifespan, but not for artist's paints. There are other methods of reducing its activity, rutile variety is less photocatalytic than anatase, organic coatings of pigment particles are worse protection than inorganic. But even the most hi-tech modern titanium white pigments are still photocatalytic. They won't degrade paint layer in months after application, but what will happen after hundreds of years?

Gigalot
03-06-2019, 05:59 AM
It may solve problems for industrial coatings with relatively short lifespan, but not for artist's paints. There are other methods of reducing its activity, rutile variety is less photocatalytic than anatase, organic coatings of pigment particles are worse protection than inorganic. But even the most hi-tech modern titanium white pigments are still photocatalytic. They won't degrade paint layer in months after application, but what will happen after hundreds of years?
i GAVE YOU EFFECTIVE METHOD how to reduce fotoactivity of titanium pigments if needed. You can use it or not, - it is your decision.
BTW, ANATASE is outdated, modern pigment is rutile form.

sarahsands
03-06-2019, 12:49 PM
Linseed, walnut and poppy oils could me mixed in any proportions, they'll dry without any problems. Safflower and sunflower oils could be problematic in mixtures - sometimes paints made with them liquefy or "melt" after a few years.
Hi Roman -

In truth Poppy Oil's numbers are worse or maybe at best equal to high linoleic Safflower Oil, which is the type you should use if making paint:

iodine value (130-140 vs 135-150)
drying index (72 vs 75)
linoleic acid (62-72% linoleic vs 70-79)

So they really should be classified and treated at a minimum the same. It is one of the bigger oversights in a lot of writing about and classification of oils that I see, even in conservation research. People usually just assume and classify Poppy as a drying oil because it was used in the past. That said, I do feel Sunflower Oil is borderline, with a range in linoleic acid that usually tops out around 60%, and an iodine number that ranges from 125-136.

sarahsands
03-06-2019, 02:00 PM
Of course. I'll cite from a couple of recent articles:

1. Franken V., Heydenreich G., Jägers E., Müller W., Schulz J., Zumbühl S. (2014) Set Back the Race: Treatment Strategies for Running Oil Paint (https://link.springer.com/chapter/10.1007/978-3-319-10100-2_22). In: van den Berg K. et al. (eds) Issues in Contemporary Oil Paint. Springer, Cham

"The liquefaction of oil paint is primarily dependent on the type of oil. Case studies suggest that semi-drying oils – sunflower and safflower oil are one of the main causes of liquefaction. Since unpigmented sunflower and safflower oil may liquefy after 5 years it seems that pigments and additives have a less significant influence on this process."

2. Zumbühl S., Scherrer N.C., Müller W. (2014) Derivatisation Technique for Infrared Spectroscopy – Characterisation of Oxidative Ageing Products in Modern Oil Paint (https://link.springer.com/chapter/10.1007/978-3-319-10100-2_15). In: van den Berg K. et al. (eds) Issues in Contemporary Oil Paint. Springer, Cham

"Ageing of modern oil paint is fundamentally different to ageing of the classical paint systems. This is strongly related to the material composition of modern artist’s paints. On the one hand, the ageing process is strongly influenced by the binder composition. Modern oil paints often consist of a variable mixture of different oils in order to control the drying behaviour of the different colours. In addition to this, general regulations with respect to the quality and stability modern pigments have changed. As a result, modern oil paints exhibit a different degradation behaviour when compared to classical oil paints. There is an increasing number of incidents where such modern paints liquefied within a few years after application (in thick layers) and drying (see Boon and Franken et al. in this contribution). This phenomenon was observed both in oil paint and in binder samples applied without pigments, fillers or additives. It can thus be assumed that the process is related to the binder composition. All incidents of paint liquefaction upon ageing so far were related to a high content of sunflower and/or safflower oil."

Full article is currently available here (https://www.researchgate.net/publication/278662954_Issues_in_Contemporary_Oil_Paint).

Hi Roman - This is one of those areas where, on the one hand, the research is definitely uncovering some stunning and concerning problems with an ever-increasing number of instances of liquifying paint. I was at the conference where these and other papers on this topic were delivered, and we are definitely engaged with the research. That said, I do think there are real issues with how the findings are being written up, the lack of some fundamental but needed information, and the way they have chosen to lump safflower together with sunflower, which I think is the more problematic component. So, just a few points.

In the first article, the examples that are shared are overwhelmingly composed of sunflower oil. Here is the table of examples found on p.337, with the only mentions of safflower oil, where you can see it is at best involved at the level of a trace:

http://www.wetcanvas.com/Community/images/06-Mar-2019/74844-table_1_-_set_the_race.JPG

Or again, in this description in a later section of two paints being analyzed:

The loss in mass of the pink paint sample (b2) which contained a high proportion of sunflower oil (~13 % linseed oil, ~70 % sunflower oil, ~17 % safflower oil) differed from the blue paint sample (~66 % linseed oil, ~23 % sunflower oil,~11 % safflower oil) (b3).

And on and on. Safflower is just getting swept up in the search for a cause, which they have connected to semi-drying oils. And we think they are on the right track but we think it is much more likely that the sunflower oil is the main driver here. Plus Sunflower Oil is borderline between semi-drying and non-drying. So at least in these cases, their examples just are not compelling for making a case against safflower. And while they do mention one sample of pure safflower oil that liquified in less than 5 years, they give no information on its specs. So there is more to find out before we can really understand if this is problematic for all Safflower Oils or simply the one they used.

In the second article, we are right back to the same samples with the same problems that safflower is just a minute presence - from p. 218:

To investigate the dripping process of oil paint (applied in thick layers), different paint samples were produced in 2003 by H. Schmincke & Co. GmbH & Co. KG, Erkrath (Germany) according to paint formulation of 1994. The paint was applied in variable thickness up to 5 mm on a paint board. The binder of the blue paint (Prussian blue) contains ~66 % linseed oil, 23 % sunflower oil and 11 % safflower oil. The binder of the light pink paint (titanium dioxide and cadmium pigments) contains ~13 % linseed oil, ~70 % sunflower oil and ~17 % safflower oil. The light pink paint contains Co- and Zr- dryer, whereas the blue paint is free of additives. Pure oil samples used in paint formulation of 1994 were applied at a thickness of 60 um in 2005

What is important to note here is the thickness of the application. 5mm is almost a quarter of an inch - and it is true that is what they are trying to understand since nearly all the liquifying examples involved extremely thick applications. But to jump from that to any implications that these issues would occur at normal brushstroke thickness is a stretch. And we would certainly NOT recommend anyone paint with safflower-based paints thickly, or for that matter even linseed-based ones. Oil paint just is not made for those types of extreme, thick textures. We believe the oil samples they mention at the end here are the ones the other article mentions, and here too the thickness is not minor, being 60 microns, or 2.4 mil. But even at that, without knowing the specs of the oil any results are impossible to interpret.

Lastly, in a third article that you did not cuite but which looked at the same painting

"Investigating Fluidizing Dripping Pink Paint on Van Hemert's Seven-Series Works from 1990-1995", p227-246

they do provide what is called the Drying Index of the paints that have liquified and place it at 72. They place Sunflower Oil at 71, and would denote a Drying Index of 70 as an oil that likely will never dry. For reference, the Drying Index of Poppy is ~72, and high linoleic Safflower ~75.

Hope that helps add some context to the complexity of the issues. We do feel they are on the right track in pointing to oils that are dangerously close to non-drying. We just do not feel that fits the profile of most Safflower Oil.

DebWDC
03-06-2019, 03:11 PM
Sarah –
I wanted to thank you for the clear and factual discussion – while showing us so clearly how misinterpretation of incomplete research so easily confounds the issue. (I deal with similar issues in my day job, and know how difficult it is.) I, and many other WetCanvas readers, greatly appreciate it. Please continue to post as your time allows – it will benefit many people.

The devil is in the details: for example, the details you provide about trace amounts of safflower oil compared to the almost 100% other oils make all the difference in our interpreting this intelligently.

Thanks again! Deb

Richard P
03-06-2019, 03:23 PM
I agree. :)

Also, makes me wonder if a small amount of wax would help liquifying paint when using sunflower oil as you recently found it helped reduce the yellowing in titanium white (I presume by stopping some of the oil to exuding to the surface).

Gigalot
03-06-2019, 05:41 PM
So, Calcium Carbonate fillers can't help paint with Titanium White to dry.

sarahsands
03-06-2019, 10:20 PM
.......One hundred years ago titanium white pigment was invented as an alternative. Now we know that its photocatalytic properties deteriorate oil paint and pigments around. Partly it could be managed with coating of pigment particles, but not entirely. Have you ever seen any artist's oil paint manufacturer who mention that they use coated Titanium White pigment? I never encountered such statements.

Hi Roman. I just wanted to chime in on this and share some research that might interest you. There has been a lot of work recently looking into the issue of the photocatalytic tendency of titanium dioxide and its impact on artwork. Most of it has been done by a researcher, Dr. Brigit Van Driel, who has a background in Materials Science and Chemical Engineering. Here are two shorter articles, as well as a link to her PhD Thesis, Titanium white pigments: Friend or Foe?

Investigating the effect of artists’ paint formulation on degradation rates of TiO2-based oil paints (https://www.researchgate.net/publication/324215467_Investigating_the_effect_of_artists'_paint_formulation_on_degradation_rates_of_TiO2-based_oil_paints)

A quick assessment of the photocatalytic activity of TiO2 pigments — From lab to conservation studio! (https://repository.tudelft.nl/islandora/object/uuid:d395afd8-9f0f-44f5-adfc-57b93ed16994/datastream/OBJ/download)

Titanium white pigments: Friend or Foe? Understanding and predicting photocatalytic degradation of modern oil paintings (https://www.incca.org/articles/publication-titanium-white-%E2%80%93-friend-or-foe-understanding-and-predicting-photocatalytic)

I'll let you explore those on your own. I would say the large takeaways are that all the cases and concerns involving photocatalytic degradation are essentially focused on anatase as well as untreated rutile TiO2. Surface treated rutile has so far proved quite resilient and resistant. Also surprising - to me at least - is that anatase continued to be used quite late by some companies; Winsor Newton did not switch to rutile until the 70s, while Talens used anatase all the way into the 90's and continues to use it in their gouache. As you can imagine, that raises some real concerns among conservators.

Finally, on the issue of whether artists' paint companies currently use surface treated rutile TiO2, the answer is a near-universal yes. You would have to go to great efforts to even find a non-surface-treated rutile sold as a commercial pigment for use in paint and would be limited to a very small, limited niche market. And no one we know of is using anatase anymore - outside of the above-mentioned gouache. If no paint manufacturers are mentioning it, we think it is simply that surface treated rutile TiO2 has so completely supplanted anything else in the artist paint industry that it is taken as a given.

Anyway, thought you would enjoy the research on titanium dioxide issues as I know that is an area of concern for you.

RomanB
03-07-2019, 01:14 PM
Sarah, thanks a lot for your replies!

sarahsands
03-07-2019, 02:06 PM
Sarah, thanks a lot for your replies!

You are really welcome! Your posts make me think and gives me an opportunity to clarify and organize my thoughts. So win win!:)

Richard P
03-07-2019, 02:09 PM
I'm surprised Talens are not using rutile across all their lines. Sounds like it's more work to maintain two pigment sources regardless of one being better or not..

Gigalot
03-08-2019, 01:19 AM
I'm surprised Talens are not using rutile across all their lines. Sounds like it's more work to maintain two pigment sources regardless of one being better or not..
Anatase is brighter and more white than rutile. Talens know that.

AnnieA
03-08-2019, 01:25 AM
I've purchased some old oil paint collections over the years, and now have a number of older large tubes of Titanium (probably Titanium/zinc), mostly Grumbacher. Does this mean they should be avoided because they may not be the rutile variety? About when did most mfgs switch to rutile? Is there any way to determine whether they're anatase or rutile?

Gigalot
03-08-2019, 04:53 AM
Anatase used in paint mainly at 1930-es. I put many swatches of different white paint on direct sun light and they are OK and can stay much time than many of organic paints. Organic paint can show discoloration more quickly than titanium can develop chalking.