This code was widely used in the 1970s, but is much less used today. (The terms bandana code, hanky code, or flagging are much more widely used among those in the leather subculture than the term handkerchief code.) It should be noted that this code has come into more general usage today.
Generally speaking, solid turns to a liquid at its melting point. Ice turns to water at 0 degrees Celsius. Chocolate melts at 25 degrees Celsius- Yum! Ice (solid) thaws when the temperature rises above 32 degrees Fahrenheit, becoming water (liquid). Other solids (oddly) vary. Generally speaking, solid turns to a liquid at its melting point. Chocolate melts at 25 degrees Celsius- Yum! Ice (solid) thaws when the temperature rises above 32 degrees Fahrenheit, becoming water (liquid).
It becomes a liquid at 75 degrees F or above, but if your room temperature is any lower than that, it will turn it to a solid. Living in the south, my homemade magic shell always stays liquid in the summertime, but in the winter turns sold at room temperature. If it turns to a solid, simply pop it in the microwave for a few seconds at a time or in a pot with a small amount of water around the jar to warm it up, therefore liquifying it.