The trick on how to make plastic look old for a high school art project is to take your time. This type of material is unforgiving so you need to do each step a number of times, little by little, until you achieve the desired results. You can always age it more if needed, but you cannot undo what you already have done. If you mess it up by going to far, you will have to start over with new material.

Take some sandpaper and lightly scuff the surface of the plastic -- just enough where you see a few small scratches and scuff marks on the item.

Soak your item in spaghetti sauce overnight. Cover as much of the area as you can with the sauce. If needed, fill a larger bowl with it and then set your item inside. In the morning, run it through the dishwasher, with no soap, on the hottest setting possible to set the stains in. This makes it look as if it was used for many years. Let it dry throughly. Repeat steps one and two until you get the desired results.

Another trick about how to make plastic look old for a high school art project is to melt it. In order to safely to do this, place the item on a microwave-safe plate and put it in the microwave. Set it on the lowest setting possible, turning it on for fifteen seconds at a time, watching it closely. As soon as it starts to sink in and change shape, turn the microwave off and let it sit for two minutes before taking the plate out of the microwave. (Make sure to use potholders to protect your hands and skin in case any of the material is still hot.) Let it cool down completely before touching it. Repeat this step until you see the results that you desire.

Add some small streaks of model paint in a rust color to your plastic item. (These small jars of paint can be found at any local craft or hobby store.) Place it on some newspaper and take your art brush, dip it in the jar and splatter small amounts on working your way around the item. One trick on how to make plastic look old for a high school art project is to splatter it heavier around the bottom of the item and lighter on top. This will give it the look of sitting forgotten in someone's workshop or basement for years. Use your paint brush to kind of blend it in. Let it dry to the touch before repeating step one by lightly sanding in the paint until it looks faded and scuffed.

Paint your item as desired to finish off the artwork. Use the same model paint that you used in step four, in the colors that you want. You can then repeat step one and sand it as you see fit. This last step in how to make plastic look old for a high school art project is all about how you want the final piece of artwork to look. Beauty is in the eye of the beholder!