Painted bear skull

Try the acetone. You can use ziplock bags filled with water (or screw top plastic soda bottles, or...) to displace some acetone. The acetone will work better than ammonia to remove paint. it sounds like you might want to go straight acetone, but if you want to try a weaker solution first, that's up to you.

 

I don't think using ziplock bags or plastic bottles is a good idea, since the acetone will probably dissolve them. By the way you can't keep acetone in most plastic containers for the same reason. You have to use glass, metal or polyethylene (look for the number 2 inside a triangle on some plastic bottles).
You could also use white spirit to remove the paint, and you can keep it in a plastic container.

 

Good point. Completely forgot about that. But, keeping the acetone in a plastic bucket is fine. Mine has been in an orange Home Depot bucket for years with no ill effects.

 

Buy straight acetone and add it to your cost. Put it in a 5 gallon paint bucket from the hardware store. Get the skull in there with at least 2 or three gallons of it. Let it sit and the paint will come off as well as loosening up the grease. After a week, flip the skull over and let the other end sit in the acetone. The fumes built up in the bucket will also be enough to loosen the paint and soften it. Try not to leave big chunks of paint in the acetone. When you are done, you can use it for other skull projects.

Spend some cash, do it the right way and impress the guy. ... And shame the other that did the crappy work. It is also possible, that the cleaner "offered" to degrease and go further at an increased cost ... and your friend refused.

 

In walmart, craft section, little glass balls, kinda like marbles.
put skull in bucket, fill the remainder with the marbles, then fill with acetone.

 

Thats a good way of saving acetone. Never thought of that!