Thinning oils.

Any good paint thinner/solvent...

If I could only use one color in oils it would be raw umber...other than that: burnt sienna, burnt umber, black and white...

to what manny said. I use white spirits to thin mine. And for washes, raw umber is a must.

HI!

I use Turpinoid orderless turpentine. I get it at Hobby Lobby with the 40% off coupon. A can lasts a long time. I agree that burnt sienna, raw umber and black are good starting points. When you get more comfortable then you can use other colors as filter washes to highlight or change the hue of the color you use them over. There are post on the forums on that too.

I personally use linseed oil to thin mine.  Its meant for canvas use but since it does NOT react with any other paints, including acrylic, I find it perfect.  I can do washes and all kinds of things with my oils without having to topcoat it first.  If you use mineral spirits or something like that it will end up messing your undercoat up if you dont seal it right.

For artist's oils I'd suggest turpentine and/or Japan Dryer. And to the list of requisite colors I'd add Payne's Gray.

I use mineral spirits for mine.  I've also used turpenoid, on reading that it's odorless, but it has a scent, too.  I didn't notice any real difference in how it worked, compared with mineral spirits.  My oils are Schminke/Mussini.

Smeagol's linseed oil is, if I'm not mistaken, the solvent or carrier used to make most oil paints, so it would make sense that it could be used as a solvent, too.

Linseed oil is a bit thick but it does thin down well when mixed with the paint and it does a marvelous job of pulling even old and dried oil paints back to life.

By this stuff, I can't recommend it enough. 

$13 retail at Hobby Lobby, so 40% less with the 40% coupon. Unless you use it to mix drinks with or want to weather your car or something, it'll last several years.

Why do I like it?

First, it flows exceptionally well.

Second, unlike other thinners or solvents, this stuff is super gentle. I've used it over unprotected enamel (Model Master, White Ensign, Floquil) with no problems whatsoever.

Third, it thins oils perfectly. Whether you want a pin wash type consistency, or you're going for a filter.

Fourth, it tastes delicious

Thats the same brand of linseed oil I have.