Can I add acrylic paint to an acrylic painting that was treated with mineral spirits?

Yes, You can add Used Acrylic Paint in Brand New Acrylic Paint

Only Dreaw Back will be Your Fresh Paint will gey Little Diluted, Because of Sprit.

Hence during next Use Either Do not Add sprit at all or Add little Less Sprit

Sprit is added in Acrylic Paint is For Adjusting Viscosity , Running Property, Or for Better & Even Coverage of Paint on the Surface(Wall)

Sprit to be added in Oil Paint Only for Better Coverage

Water Good Quality should be added in Water Based Acrylic Paint

Water Based is Water Soluble Paint to be used Water for Washing the Brushes

Oil Paint is Oil( Sprit) Soluble To be used sprit to washes the Brush

Regular varnish won't take anything off an acrylic painting. Regular varnish is thinned with MINERAL SPIRITS...It's superior to acrylic varnish hands down.

Painting over the mineral spirits may be problematic. Depends on how long ago the mineral spirits were used.

Get a soft cloth, and dampen it with Isopropyl Alcohol, and gently wipe down the areas you want to paint. That should remove any residue enough for you to paint over it.

If you properly varnish the work when you are finished, it shouldn't flake.

You might try rubbing off the excess mineral spirits using a good soft cloth with soap and water and then drying it with a dry soft cloth. When the picture is dry, spray clear acrylic sealer over the entire picture and let it dry. Then , add more acrylic paint where you see fit. When this new paint is dry, re-spray the entire picture with another layer of clear axcrylic sealer. This sealer will seal anything to make it permanent and bring out the "brightness" of the colors. It can be purchased at an art or craft store or wal-mart in the craft section.