Here I want to share my experience with removing old or failed paint finishes without harming the model.
In my opinion, the best method to remove old color is using spirit or rubbing alcohol. It works both for acrylics and enamels. Spirit is essentially the same as ethanol, which is an alcohol like propanol.
- acrylics: any alcohol is dissolving the paint immediately. With thicker layers of color, it is a good idea to soak the model for some time before removing the color with a brush. Resin ans styrene does not suffer from this treatment, I removed the finish of a resin figure three times in a row without damaging the details.
- enamels: For removing enamels, the model has to be soaked for some time. The color then flakes from the ground in different sized chips. Any remaining color can be removed with a brush.
I am very happy with using alcohol or spirit to remove paint. The first finish of my king tiger (including a layer of Tamiya primer) was completely removed with this method. It is simple and the fumes are tolerable. I would rather not try to use others methods like brake fluid or oven cleaner.
You should also avoid using white spirit or turpentine to remove enamels. The color is removed, but turpentine is also detracting softening agents from the styrene, leaving the model brittle and with cracks and fissures.