If you accidentally leave a plastic spoon laying on a warm oven range, it may melt into a puddle and virtually fuse itself to the enamel. If you mistakenly microwave a plastic dish that isn't microwave safe, it can melt right onto the glass turntable. These plastic blobs can be some of the toughest stains to tackle.
Allow the area of melted plastic to cool completely. If the metal or glass surface is part of an oven or toaster oven, make sure that the heating element is turned off and the entire appliance has completely cooled before proceeding. Melted plastic that is still hot can cause severe burns if it touches the skin, and the stains are actually easier to clean if the areas are left to cool completely.
Soak a dishcloth in household ammonia. Gently wring out some of the excess, but do not wring it out completely. Lay the soaked cloth on top of the melted plastic. Allow the stain to soak under the cloth for at least 15 minutes.
Remove the ammonia cloth. Rub at the plastic with a dry, soft dishcloth, applying firm pressure. This won't remove many melted plastic stains, but it's usually worth a try because the cloth is the least abrasive tool. If this doesn't remove the plastic completely, move on to the next step.
Rub the plastic firmly and briskly with a synthetic scouring pad such as the green side of a green and yellow kitchen sponge. This will remove most melted plastic stains. If most of the plastic comes off but a little bit of residue remains, you can re-place the ammonia-soaked cloth for another five minutes and try again with the scouring pad.
If the scouring pad does not work, switch to a plastic scraping tool. Windshield ice scrapers work well, and so do credit cards and other laminated cards. Just be very careful not to scratch the surface you're cleaning. Softer, more pliable plastic scrapers are less likely to cause damage than firmer, thicker ones.