Sun thickened linseed oil is a created by exposing the oil to the sun to create a thick syrupy somewhat bleached oil with similar brushing qualities to stand oil.
Drying oil painting in the sun.
In general i agree with what has been said so far its not a good idea to leave an oil painting in full sunlight for an extended period of time this will affect certain pigments.
6 mix your paint with a solvent like turpentine or liquin.
A couple of other things to think about that.
How to make your oil paintings dry quickly.
To minimize debris getting in but so that the air can flow through.
To speed up the drying time you can turn on a.
This process is demonstrated in the painting below.
Buy some commercial paint hardener or dryer to dry paint in a hurry.
Add absorbent materials such as sawdust or cat litter to the paint if there is more than just a little left.
I typically find this is not such a good method as the paint dries too.
Two paint using thin layers and washes which will dry reasonably quickly.
Stir it periodically to hasten drying.
Use alkyd white instead of normal white to mix with your oil paints.
Not direct sunlight due to fading and too much darkness will cause it to yellow.
Pour paint from a full can into other cans or containers a little in each so it dries quickly.
Oil paintings need daylight.
Use an alkyd medium with your colors.
When i start an oil painting i will usually thin the paint using odorless solvent so that it becomes a thin wash with a watercolor like consistency.
Also paint is slow to dry in a cold environment so a warm room is preferable.
Bugs will get stuck to it.
One leave the painting to dry in a well ventilated open area where air circulates a fan helps.
This will make your paintings dry in a day or two compared to a week.
This layer of paint dries quickly within 24 hours.
Since linseed oil dries faster than other kinds of oil mixing a little extra linseed oil with the paint on your palette can help speed the drying time of your painting.
However there is an important exception and that is when an old painting is suffering from discoloured or yellowing of the varnish layer.
After that i embrace the slow drying time of oil paint rather than try to avoid it.
Combine linseed oil with the paint on your palette.
As you may have guessed from the prior answers drying an oil painting in the sun is the wrong thing to do.