Acoustic Day-to-Day Resource
http://www.guitartips.addr.com

I went into a music store once and saw an old Martin guitar hanging on the wall but there was something very different about it. The front of the guitar had cracks in it but the cracks weren't in the wood and did not follow the grain of the wood. It looked like cracks in a sheet of ice or glass. I asked the owner of the store what it was. He was obviously trying to sell the guitar so he told me it was a normal condition that happened to all acoustic guitars.

At this point, I became skeptical and did a little research. This condition is called checking and occurs in the lacquer finish because the guitar got too cold and then was warmed up too quickly. This is definitely a problem to look out for when buying a guitar.

If you have to take your guitar out in the winter cold, keep it in it's case until you get inside a heated building. When you get inside the building, try to let it warm up in the case for a while before you take it out. This will allow it to warm up more slowly and help prevent checking of the finish.