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Weighing In on the Drying of Oils

11 thoughts on “Weighing In on the Drying of Oils”

    • Hi Charles. The drier was a standard manganese cobalt mix that is commonly used to adjust oil paints. Most painters will usually find it pre-diluted with solvent to allow for easier use but we used a solventless concentration.

      • Thank you so much. The problem is, I can’t find any information on the actual concentrations in these diluted driers! Cobalt Tillate and D-Limonene, for example, is pre-diluted, but to what?? And the instructions say “..[use] small amounts.” and “test before using,” etc. I just so happened to have a Grumbacher drier, and it’s rather an emergency (show).

        What’s the dilution, 10%, 1%, .01%? I spent hours looking online; It should be everywhere. I want to know how many molecules I’m using!

        So I made a 1% solution just to be safe, and used what amounted to a .005% solution based on reading your article, but for all I know, it was a .00005% solution. I haven’t a clue, and I can’t find the information. Where am I supposed to look? I’d be willing to go out of my way to buy a Wiliamsburg drier if I knew what was in it, but what otherwise would be the point?

        Your article is fantastic reading, despite the the redaction which I understand might be required proprietary secrecy. But please try to share more, if you can. Thank you so much!

  1. Hi Sara, I’ve just discovered this informative and precise article, I hope it’s not too late to ask a question.
    My attention was caught by the sentence: “highly reactive free radicals were being spun off, along with unstable hydroperoxides that quickly decomposed into an array of often-volatile components”. Free radicals are usually regarded as very unhealthy, at least when ingested. Are they equally dangerous when inhaled? Is the mere smell of an oil painting somewhat harmful? When I paint in oil I avoid solvents, which implies that I use some more oil, so I’m interested in this subject.
    Thank you.

    • Hi Mario – Sorry it took me a while to see this and respond. The free radicals being spoken about in the article are limited to the chemical reactions happening within the process of oxidization and do not represent anything to be worried about. Free radicals tend to be very short-lived and are associated with a wide variety of common and essential processes. For example, many forms of combustion such as the common one of fire involve free radicals as part of their process. So, while we continue to advocate for reducing solvent use and exposure, to improve health and safety, the chemical processes involved with the curing of oil paint is not an area of concern.

      • Thank you for your answer, Sarah (and sorry for misspelling your name in my former comment).
        Looking forward to your articles here on JustPaint.

  2. Nice reading this again (is all of Just Paint now online with this nifty commenting feature?). Since first reading it – probably my first introduction to how oil paint dries – I’ve learned a bit more, so now I am curious about something:
    You briefly mention that you also did tests with blanc fixe and calcium carbonate, how did those turn out?
    (And how about the zinc oxide?)
    An article focusing on “through-driers” would be really interesting. As would an article about using small amounts of umber etc as drying helpers…

    • Hi Tona –

      We are glad you enjoyed reading the article again within this new format, and yes, all of Just paint is now offered in this way. So please feel free to explore and rediscover all of the past articles, as well as subscribe so you can know when new ones are published. Currently we post two a month online, and will continue publishing a print version at least once a year.

      As for your questions, the inclusion of blanc or calcium carbonate did seem to introduce small differences but the testing was too limited to be conclusive and so additional testing will need to be done at some point to tease apart the data more. Especially useful would have been testing films of these materials alone, as compared to Titanium White, and also to look at how they might impact other pigments beyond just titanium white. So, while included in the initial testing, we placed that data off to the side for further exploration and focused more on just the differences in oil and the use of driers. Zinc Oxide is a similar story – some differences were seen but would need to focus more directly on zinc’s impact at different levels and in different systems before we could conclude anything. In terms of drying, in thin films id did not seem to have a large impact, but in very thick ones it did slow things down, which is not surprising or unexpected.

      Thanks for the thoughts about future articles. We think both of those topics would be great to explore and will add them to the wish list. Would only want to at least point you to a couple of blog posts on the use of umber as a drier in Williamsburg’s Van Dyke Brown and Cassel Earth:

      When is Long too Long a Time? On Van Dyke Brown and the Art of Drying

      French Cassel Earth: Bringing it up to Speed

      Hope the above is helpful and as always, if you have any other questions, just ask!

  3. Hello. Of course, since ancient times it is known that the oil dries unevenly and that lo varnishing paintings need to wait a year or even a year and a half. But your graphs are very clear and informative show the process. I have to you questions:
    1) figure 2 shows, that Stand Oil is behaving more predictably. Is it preferable to use it in oil paints?
    2) Almost all artists use so – called “doubles” or “tees”, that is, mixtures in different proportions of oil, solvent and varnish, and sometimes just add only varnish to the oil paint-and all this in order to achieve uniform drying of the oil film. Are there any of your studies that would take into account such additives, for example, at least varnish?

    • Hello Ruslan,
      It is difficult to say why stand oil absorbed oxygen more slowly than the other test batches. It does have fewer unsaturated bonding sites than the other drying oils and it is much more viscous. Typically, stand is not used to make oil paints because it makes a very sticky, stringy, slower drying oil paint. It’s use as an additive/medium to the paint can impart a nice gloss and it is thought to yellow less over the long term than regular linseed drying oil. As for your second question, we have not tested drying rates and variability in the oil paint films with varnish additions as one of our factors. You can read and learn more about different varnishes and mediums on MITRA – a conservator moderated forum and resource about artist materials. You may have to register to see all their resources and post questions and read the backlog of answers. You can access their site here: https://www.artcons.udel.edu/mitra
      Best Wishes,
      Greg Watson


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