Home › Forums › Explore Media › Oil Painting › The Technical Forum › What are the drying agents in paints?
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August 12, 2018 at 5:59 pm #460378
Manufacturers add drying agents to slow drying pigments. Some lines, like Lukas 1862 and Duo have drying agents added to their whole line. Anyone know what the drying agents are?
Mayer says that the most common industrial drier is cobalt, but is vague on typical industry practice. He also says that if a hand mulled paint is especially slow drying, the drier should be added to the oil when the paint is mulled, but doesn’t give any details about what to use or how much.
Also, if the industrial driers are cobalt, isn’t that bad for our paintings?
August 12, 2018 at 6:17 pm #674681%
August 12, 2018 at 6:32 pm #674682But, fortunately, we can use non-industrial driers and they can give better result than deep colored and smelly industrial stuff!
The modern Cobalt drier was born in 1920 year and it gives most happy way to quickly make our paint tacky and to let it wrinkling and yellowing.
August 12, 2018 at 6:39 pm #674678There have been a number of driers added to paints over the years, most often siccatives in liquid form that are added during the process of grinding the paints. When the oil is added to the paint, so too is the liquid drier, then ground in with the same mills or mulling tool. The result is a paint that will dry faster, to slow drying generally slower drying fillers are added, these are generally powders or sometimes they are ground in a slower drying oil.
- Delo DelofashtAugust 12, 2018 at 7:01 pm #674689The most common drying agents in oil paint are drying oils, such as Linseed and Walnut Oil, these are naturally drying agents.
Pigments such as Umbers contain manganese, which accelerates drying. Certain resins can also be mixed to the paints, this will make the drying time shorter, among them Dammar, Alkyds, and in special cases the expensive Amber.
Lead, Sugar of Lead, which are normally used to create varnishes, can also be used to modify oils by cooking them in powder form for a few hours. Stirring must be continuous for a complete integration.
August 13, 2018 at 5:49 am #674683I think, that people who started as acrylic painters and then switched to oil paint, are looking for “fast drying” oil paint forever until the end of their artistic development.
People who started with oil paint and then unfortunately switched to acrylic due to health issues, they are looking for slowest drying “open acrylic” forever until the end of their health issues to switch back to oils.
Artists who started with oil and then tried acrylic after having good skill, and they can combine both into one painting are most happy artists because they know secrets how to paint well with both oil and acrylic mediums.
Artists, who decided to avoid acrylic due to a traditionalism ideas, they are looking for slowly drying oil paints and they are a Clove oil users and Geneva oil paint fans.
August 13, 2018 at 12:33 pm #674690Wikipedia has an article titled “oil drying agent.” It is useful, but not very extensive. Here, “drying” means “curing by polymerization,” rather than by solvent evaporation.
Plant seed oils are used as food by the developing plant embryo. The oils are not as useful if they become polymerized. So, a drying oil does not naturally dry at a rapid rate, because the seed coat is not perfectly impervious to air and light. From the plant’s perspective, it would be better if the oils did not polymerize at all; but it suffices if the rate is slower than that of seed development.
Drying oils are catalyzed (the reaction runs faster) by certain contaminants, most often divalent metal ions. Divalent metals ions are quite common in mineral compounds, including most traditional pigments. But especially among the modern pigments, there are no divalent metal ions. Some manufacturers will add a touch of divalent metal ions (usually an organic cobalt compound) to those colors that do not naturally have them, in order to make the drying rates of various colors more equal. Other manufacturers don’t do that.
Lead White (Lead Dioxide) will release some divalent Lead ions, and is a very effective drying agent (siccative). Many natural earth pigments, especially those with some Manganese contamination, are also very effective siccatives. Modern synthetic earth pigments may be too purified, thus less effective as siccative. Although Iron is (often) a divalent metal, many forms of Iron Oxide are ineffective as siccative, because the Iron is too tightly bound to the oxygen, and is not released.
One problem with divalent metal ions is that they usually add color. Cobalt adds purple; Iron (if in a suitable compound) would add red; Copper would add green. Lead is more colorless, but subject to long-term change due to atmospheric contamination.
Cobalt is a “primary” siccative, meaning that it directly catalyzes the reaction of atmospheric Oxygen with the oils. Others, such as Zirconium and Calcium, are “secondary” siccatives, meaning that they improve the way that Oxygen is distributed within the curing paint. I have never quite understood that.
The compound Cobalt Napthenate is widely used. This is an organic compound (napthenate) that will readily mix with oils, and will release some of the Cobalt.
I add a little bit of a product named CoZiCa to the inexpensive mass colors (white, etc.) on my palette, and to medium. I do not add it to the expensive colors (PY128, etc.) that are used only as additives to other colors. CoZiCa has Cobalt, Zirconium, and Calcium. This way, only the cheap colors risk drying on my palette before I get a chance to use them. The expensive colors are always mixed with a cheap color at moment of use, so they get their dosage of siccative that way.
If you wish to prolong the lifetime of colors on a palette between sessions, refrigeration is very helpful.
Note that Alkyd oils have different technical considerations. But if you are using an oil medium with “just a touch” of Alkyd added, then the above considerations still apply.
August 13, 2018 at 1:43 pm #674684Zirconium and Calcium, are “secondary” siccatives, meaning that they improve the way that Oxygen is distributed within the curing paint. I have never quite understood that.
Lead is more of a secondary siccative rather than primary. The secondary siccative is a reagent, that can react with Azelaic diacid into oil paint films.
August 13, 2018 at 2:06 pm #674691Thanks everyone, that was very helpful. The recent discussion of Spurgeon oil has made me want to learn about paint making and chemistry.
August 13, 2018 at 4:37 pm #674685Thanks everyone, that was very helpful. The recent discussion of Spurgeon oil has made me want to learn about paint making and chemistry.
Spurgeon oil is a legendary and mysterious product of deep water/alcohol refining process. It’s a second famous legend after Asterix and Obelix druids Drink!
August 13, 2018 at 4:40 pm #674692Yes, I read a vigorous debate thread about it!
August 13, 2018 at 5:03 pm #674679Ah yes, that was such a great debate! That was good fun.
The study of oil, chemistry, and the effect on paint and paint making has made me a much better user of the paints I own. Now, I have so much better control and can adjust the properties of paints easily, because I understand how the paint can be modified to achieve a given effect.
- Delo DelofashtAugust 14, 2018 at 6:44 am #674686In theory, extremely pure oil is less yellowish. I have a link to scientific paper (in microsoft word doc) about that phenomenon:
http://www.viks.sk/chk/studcon_2_01_121_131.docAugust 14, 2018 at 10:10 am #674693Is there any truth to the suggestion that mixing a small amount of violet in white paint will visually cancel future yellowing?
August 14, 2018 at 12:06 pm #674687Is there any truth to the suggestion that mixing a small amount of violet in white paint will visually cancel future yellowing?
It might be better to use Permalba White. It do not yellows.
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