Oil washes done with Gemini odorless mineral spirits have resulted in semi-glossy spots. So I did an experiement on an old unfinished model w/ W&N oil paints. I left a small amount of the oil paint on a cardboard for several hours to remove linseed oil as much as possible.
Gemini: Unless oil washes are very thinly applied, they result in semi-glossy spots. Even when completely dried for 48 hours, some spots remain semi-glossy. The semi-glossy spots are visible through 3 coats of Vallejo matte varnish!
Mona Lisa odorless mineral spirits: No matter how I apply oil washes, the result is "flat."