Candle tunneling is when a candle has a ring of un-melted wax around the perimeter. 

Many things can cause tunneling which include the candle not having a properly sized wick, to drafts affecting the burn efficiency, to not trimming the wick each time. In most cases, tunneling is caused by not burning the candle long enough.

Who knew there was a proper way to burn a candle?!

Here is an example of a candle that is tunneling:

This was a candle I was burning in my studio with the ceiling fans on. The draft from the fans impeded the burn. Meaning that it blew the wick around so that it couldn't do it's job properly. Normally this candle would burn edge to edge in a calm environment.

Here is what a candle should look like if it is burning properly in good conditions:

In this photo you will notice that the entire top surface of the candle is melted. When enjoying a candle is imperative that each time it is lit, the entire surface melts. This ensures that the candle won't tunnel. 

When a candle tunnels, it leaves behind a ring of wax that can't be enjoyed. The wax is what feeds the wick and provides hours of enjoyment. When a candle tunnels, you get fewer hours out of it.

To learn how to get the most from your candle, head to this blog post for four tips on proper candle care.