It is a great idea to save leftover paint for future touch-ups, but proper storage is imperative. To keep the water in and the microorganisms out store it in an airtight container. You can use the original can or transfer the paint to a clean jar with a screw-on lid. Keep it at room temperature. Texas heat will kill paint so don't put it in the garage or shed!
How to tell if it has gone bad? If the lid is popping up or the can is bulging microorganisms are eating the paint and giving off gas. Other signs that a paint is past its prime include a thick, rubber-like film topping the paint, or when the paint won't mix well or stay blended.
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