I would take it to a gallery that sells paintings. They could look at it and tell you if you can do it or have it done professionally. I would not mess with any home remedies etc.

Me either, no home remedies for cleaning. I have used a white pencil ereaser to clean an oil paintings white liner tho.

I'm a collector and have had luck with a very mild mixture of ivory soap and water when I've needed to clean some of my prizes. But...use an extremely light touch. Never scrub or use any abrasive tools! And...if possible...try this solution in an area of the painting where it won't show...like a corner or folded over canvas on the frame...if that exists. Just wet the rag, squeeze it out to a semi dry state and dab away. If the rag turns the color of the suspected grime...you'll know it's working. This treatment is best for oil paintings only. Unless you are absolutely positive that the artist used 100% oil paint...do as suggested above and consult with a professional cleaner.

Above all...don't use the lemon solution. Lemon contains an acid [citric acid] that could do harm.

The only other solution I've used with good results is a mild mixture using Simple Green and water but for recommendation purposes...I'd prefer that you stick with the ivory soap solution.

Once the canvas is clean...use clear water on a clothe to remove any of the soap mixture and gently dry the canvas with a dry clothe.

HTH

Anne

The yellowish color might be aged orange shellac. It won't clean off if it is.
I have cleaned oil paintings with a very mild solution of Murphy's Oil soap and water (and you can clean walls with it too). Use a mild soap in more water than the bottle calls for and an almost dry wrung out rag. I would blot, test in an inconspicuous place. The paintings I cleaned were damaged by smoke from fires. Some were damaged beyond repair, but some were saved.
If you really want to do a test, but an old painting at a thrift store and try a bunch of methods.

Go to Hobby Lobby and buy a product called an art gum eraser - it's made especially for cleaning up a painting. I have oil paintings and it works to clean them - just gently rub it over the spots. Try it in an inconspicuous spot to see if it works for you.

kathy has the right idea, in fact oil paint (white and light pigments) tend to yellow over time due to the linseed oil used as a painting medium, esp. older works. You won't be able to lighten or whiten these areas.

Thanks everyone for the help. I really appreciate it.

I want to thank everyone for your suggestions. I do really appreciate them.

I have replied twice with this " thank you" and neither one showed up. Sorry about that. We'll see if this one does.

thanks again