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Rubbing alcohol, acetone, and paint thinner are all great options. You can also use a household cleaner with pine oil in it, like Pine-Sol. If you’re using rubbing alcohol, be sure to get the highest percentage that you can find: 91% or 99%. If the percentage is lower than that, the rubbing alcohol won’t have any effect.  If you have sensitive skin, it would be a good idea to wear plastic or vinyl gloves. Acetone may damage some types of plastic, such as Plexiglass or vinyl-based plastic. It’s safe for fiberglass and polyester resin, however. This is important, because different types of plastic react different types of solvents. Pick up a drop of your solvent with a soft paintbrush a Q-tip, or even a toothpick, and place the drop onto an inconspicuous area on your item. Wait a few minutes, then rinse the solvent off.  If nothing happens to the plastic, the solvent may be safe to use. Keep in mind that some solvents may need hours before they have an adverse effect on your item. If the plastic changes color or texture, don’t use the solvent. You might even want to press the area with your fingernail; if you see an indent, choose a different solvent. This will work the best with acetone, but you may be able to use rubbing alcohol as well. Simply soak your cotton ball with your solution, then rub it across the painted area until the paint comes off.  Discard the cotton ball when it gets dirty, and use a new one. Acetone evaporates fast, so you’ll have to re-soak the cotton ball often. If you don’t do this, the fuzz will stick the the paint. If the cotton ball is not working, pour your rubbing alcohol or acetone over the painted area, then scrub it with a stiff-bristled brush. Keep applying your solvent and scrubbing until the paint comes off. Avoid nylon brushes if you are using acetone, or the bristles may melt. Place your item into a container, then fill the container with enough of your solution to submerge the item. Leave the item in the solution for 15 to 60 minutes, then pull the item out. Scrub the paint off with a stiff-bristled toothbrush or manicure brush. Clean the item with soap and water afterwards, then let it dry.  This method works best with paint thinner and household cleaners. You can soak most plastic items in household cleaner for up to 24 hours.  If there’s still residue on the item, dip it into the solution, then scrub it again. Think of this as scrubbing dried food off of a plate.
Choose your solvent. Test your solvent in an inconspicuous area. Wipe small areas down with a cotton ball soaked in your solution. Use a stiff-bristled brush for stubborn stains. Soak fully-painted items in your solution, then scrub the paint off.