Will raw sienna help oil paint to dry faster?
My tube of WN titanium White takes forever to dry. I’m thinking to add a bit of RS to a lump. I know it will alter the color a bit, but in this instance, that’s not a problem.
I just want it to dry before next year!
Will any of the earth colors have that drying effect? The umbers do.

There are so many Titanium Whites from which to choose, when selecting a brand, you certainly don’t need to settle for one that doesn’t exhibit relatively normal drying times. In my experience, Winsor & Newton is a mediocre brand of paint, and since they have chosen to employ Safflower Oil for many of their lighter colors, because of some fear of yellowing of the Linseed Oil, the drying has undoubtedly been compromised. Safflower is a much slower drying oil, and can lead to the applied paint requiring an inordinate length of time to dry, once applied to a canvas.

I sure would not be tempted to accommodate a slow-drying White paint by compromising the color by adding faster-drying earth pigments to it. One should never compromise the color of an oil-painted passage merely to “correct” some sort of deficiency of the paint, itself.

Just purchase a decent Titanium that behaves, and dries as it should.

I would recommend seeking the “Art Treehouse White” from The Art Treehouse. Good paint! Does not overpower colors, when mixed with them. Dries very appropriately. Opacity, and handling is very close to Lead White. Although it’s binder is Walnut Oil, a slower drying oil than Linseed Oil, it still dries within a normal time, compared to some of the other White paints.

https://arttreehouse.com/artstore/

An alkyd medium such as Galkyd, Liquin or Gamblin’s Solvent Free Medium will greatly speed drying times of whites and other slow-to-dry colors.

I have to disagree that W&N paints are mediocre. I have found the prices are very good and several paints I have in their range are excellent.

1. I wouldn’t call W&N mediocre (sounds insulting), more like “average” for artist quality (not insulting). If you want better (say, very high pigment density) then you have to pay more, or shop very carefully. As already noted, the culprit is safflower oil, which is also used in a variety of whites made by other manufacturers, including some fancier than W&N.

2. An alkyd medium will speed things, but not necessarily by much, because it depends on how much you use. The more medium, the less covering power (opacity) of the resulting mixed paint. Galkyd and Liquin have a lot of alkyd, and have solvent (because that much alkyd wouldn’t dissolve without it). The solvent-free liquid (or gel) has a much smaller amount of alkyd, and may also be based on safflower oil. Any of these products probably contain just a touch of siccative, that’s my guess.

3. I use siccative, namely CoZiCa. Very tiny amounts. Warmth also helps a great deal. I add a little CoZiCa to some medium (in my case, solvent-free gel), then add a touch of the medium to the paint at the time I am ready to use it. This technique makes it easier to dispense a tiny quantity of siccative, and also prolongs the usability of unmixed paint on the palette. The siccative itself has long shelf life in an opened bottle.

4. Just as with any ordinary medium, the gloss of paint will depend on how much you add. So your painting may have duller and glossier areas, which you will need to make more uniform as a final touch.

Short answer to your question, yes. Technically speaking, Sienna and Umber are the same pigment, and will have a similar effect on paint films. I cannot see a reason to pick Umber over Sienna for the effect you are seeking to obtain, maybe someone else could enlighten us as to a reason though.

Many divalent metal ions are siccatives. Mn++ (Manganese) is a divalent metal ion. However, if the metal is so tightly bound to its pigment molecules that it cannot partially sneak away as ions, then it will not have much of a siccative effect.

Iron Fe++ would be a strong siccative. But Iron Oxide pigments are not siccatives, because the Iron is so tightly bound to the Oxygen. The ions cannot escape. It is possible to make Iron-bearing organic molecules that release some Fe++ for siccative action, but there’s no advantage to it, since there are better alternatives. Prussian Blue is Ferric Ferrocyanide, with Fe++ and Fe+++, but only the Fe+++ has much mobility.

It is possibly the case that the various Umbers and Siennas not only have different amounts of Manganese, they have the Manganese more or less tightly bound.

Calcium Carbonate has some siccative action, because under many conditions some Ca++ can sneak away from the carbonate part. Doesn’t need to do it permanently.

Interesting guys, though I would be reluctant to rely on Mayer’s outdated information. No offense intended, it is 30 or more years old at this point, the data for which was probably taken over the decade preceding that. Paint formulations have improved greatly over the last few decades.

Pinguino, indeed that is how the chemistry works, and as I understood it. Umbers from some sources can indeed contain a greater quantity of Manganese than some Sienna pigments. As an additive drier that well might increase the drying speed faster than Sienna, but it’s worth knowing why and not just what, wonderful side effect of threads like these.