Ultimately, we can't tell you exactly how long you can leave butter out. We have no problem with leaving butter out to soften as long as it is well-covered. It usually doesn't take us more than a couple days to go through a stick anyway! We've never had rancid butter in that time.
For complete instructions, see my weekly column. Note: The vinyl melts in just a few minutes and is warm to the touch when you pull it from the 200-degree oven (don't use a hotter oven or the vinyl will start releasing toxins). You can form it by hand immediately, but use leather gloves if you're nervous. All beginners in Record Upcycling should try a bowl.
Two elements are liquid at room temperature (298 K): Bromine (Br), an reddish brown liquid witha suffocating odor, melts at 265.9 K. Mercury (Hg), a toxic metal, melts at 234.32 K. (See Why is mercury a liquid at STP?) Four elements melt just a few degrees above room temperature. Francium (Fr) , a radioactive and extremely reactive metal, melts around 300 K. The false color image at left shows 10,000 francium atoms in a laser trap.