clean paint brushes used for art work after painting with oil paints? The brushes have become very greasy and the paint wont clean off.

I would suggest a solvent such as mineral spirits, and maybe lacquer thinner. But use outside in the open air, and don't breathe the vapors.

Use paint thinner, preferably odorless.
After you get the bulk of the buildup out of the bristles you can then use ordinary dish soap to clean the brush thoroughly and shape the bristles back into their original shape, before laying the brushes flat on their sides for storage.
If you sore the with their bristles down it will bend them undesireably. If you store them bristles facing upwards the paint thinner will remain within the ferrule (the band of metal which holds the bristles in) and will weaken the bristles over time.
Hope this helped!
Jim

turpenoid is odorless and works perfectly. In my art class we would fill a jar half way with the turpenoid and put a hole in the top large enough for the brush. Place the brush in the hole so that the brush is in the turenoid but not hitting the bottom of the jar which will ruin the shape of your brush. It should stay pretty well and clean your brush well too.

as salaamu 'alaikym, my friend.

First clean them with Turpeniod ( a turpentine type cleaner that is a bit less harsh and is what you are already using with linseed oil to mix the solution you use to dilute or thin your oils.)

Next, wash them with a bar soap, like Ivory or some other mild body soap. Work the lather all the way through the bristles, rinse and then reshape the head of the brush and allow it to dry in that shape.

If there is paint on the handles, simply scrape that off.

Ma'a salaam

u have to use turpentine or white spirit to clean them. or u can buy water soluble oils that clean and thin with only water. i reccommend the artisan brand