Back when I got my 1st microwave (many years ago) the instruction booklet showed how to test for this. Fill a cup that you KNOW is safe with water, then put that & what you want to test in the microwave and run for 30-60 seconds. The water will heat up. If the dish is cold (room temp) it is safe, if a little warm put a bigger cup of water, let dish cool down & try again. If cooler, it should be alright. If dish has a style or model number, try contacting Corning online & ask them, to be sure.
Not recommended. I think cranberry glass, even Corning's, was originally made for decorative/ornamental use only. Unless it's cookware that says, "Oven &/or Microwave Safe" on the bottom, don't heat it.
You can use your glass Corning ware in an oven or a microwave. Corningware is now making more pieces that can be used in microwaves and ovens because of the durable material they use in the wares. You should first clean it before you place it in the microwave and make sure that you do not heat small amounts of foods since it would cause excess heating on the material.