My Vasari Sap Green takes forever and a day to dry to the touch…:eek:

I’ve got my listening ears on for this topic… thanks for bringing it up Carey.

The subject is fairly complex, or rather, prone to variables.
Primarily, the question is one of oxidation and oil content. The more oil present, the longer paints take to dry. Paints that take a long time are transparent colors, reds, yellows, and blacks. Also, titanium white can take a long time.
Pigments that dry quickly are usually earth colors and iron oxides, particularly the umbers which have manganese as a natural siccative (drying agent).
Mars Black is faster drying than Ivory Black, which in turn is faster than Lamp or Carbon Black. In the case of Mars, it is a chemical advantage of iron oxide. The other two are largely oil content affecting drying time.
Cobalt pigment is also a natural drier, so mixtures with cobalt blue will dry more quickly than most other blues.
A common misconception is that lead pigment accelerates drying times. This is incorrect unless driers have been added.
Temperature and air flow also play a part in speeding drying, with temperature being the superior force. Paints can dry in less than half the time if “dried” at 75 degrees F, compared to 55 degrees F. Roughly, “normal” paint may take up to two weeks to dry at 40-50F, and 1-2 days at 70-90F (overnight low/day high).
The quote above, “thick impasto oils will take up to six months,” on drying times in misleading. It doesn’t take six months for impasto oils to dry — they are surface dry in slightly longer times than thinly painted areas. But the interior, far removed from oxygen in air, can take several years to completely dry. But that is really academic to the use of varnish and further paint layers, which can be pursued in the normal time frame.
Average or normal drying times for “average” thickness of layers will be 2 to 4 days. Thin passages can dry overnight. Addition of umbers can dry paints in less than that time.
The use of siccatives is recommended for fast drying of all oil binders, including poppy and safflower oils. Common driers are lead napthanate, cobalt, manganese, and mixtures of these chemical driers. Also alkyd oils dry more quickly than regular oils, but will accelerate regular oils when mixed in. Same for quick drying alkyd mediums.
With the use of siccatives or quick drying mediums some oil paint layers can be safely overpainted in as little as six hours without disturbing the underlayers (gentle brushing, of course!).

A common misconception is that lead pigment accelerates drying times. This is incorrect unless driers have been added.

Just to elaborate, I’m sure Gun know this, but lead IS a siccative in many forms like lead oxide, massicot, litharge ect. The “misconception” is assuming that lead carbonate aka (flake white or cremz white) is an oxidizer or powerful siccative. Cooking lead carbonate does convert it into a oxidizer (aka siccative) or more specifically pbo as in recipes for black oil.

Another factor on drying is surprisingly (at least to me) light. Oil paint drying in the dark will take longer to dry than paint exposed to light, ambient or direct.

Below is a table of drying times I pulled from Robert Massey’s book. (# = parts Pigment – 1 part oil by volume)

Some of these pigments drying times are easy to explain like for the umbers or Burnt sienna. These pigments have natural oxidizers or siccative that speed up the oxidation process.

The lead, titanium, or zinc whites dry moderately fast imo because of how lean they. There is very little oil there to dry.

Alizarins, Ivory black, and phyalo greens are slow driers imo because of how fat these pigments are. These pigments require a lot of oil to form a paint and are also the pigments that tend to crack as well if not careful.

The mystery to me is why a cadmium, vermillion, or ylw ochre are such slow driers. They aren’t particularly fat or lean pigments, yet the drying time is significantly different than other paints I would have assumed comparable. At this time I assume it’s either that these pigments have a natural anti oxidant present, or since light is an ingredient in drying time, it may just be how light is absorbed with these pigments that makes the difference.

My Vasari Sap Green takes forever and a day to dry to the touch…

Kinda hard to comment. I’ve heard from gun that they have a chart that list their pigments they use, but I’ve never seen one. I assume that this sap green is made of ultramarine and a synthetic Indian ylw. Both pigments known to be slow driers. Why exactly its slow drying I dunno.

Both litharge and massicot have a long history of being used as a pigment/paints. Its only in modern times did they lose favor. Bit of trivia, but in the mid west if you can imagine that typical farm with a rust red silos or barn. That’s actually red lead, aka litharge or pbo4.

As for the list, I don’t know how accurate it is either. I’ve never spent any time tracking drying times of all my paints & doubt I ever will. Can say though after mixing paints and observing what an unmodified oil paint acts like, the efforts made by most paint manufactures to get paints to act similar to each other and dull a lot of their specific characteristics is a lot more obvious now. With unmodified or less processed paints, fast drying pigments seem to dry fast, slower drying pigments seem to dry slower and all those individual characteristics stand out.