The combustion process can leave behind black soot on propane gas logs. This usually adds to the logs’ realistic appearance and does not pose a problem. Liquid propane log sets typically produce more soot than natural gas log sets. This is completely normal. If a vent-free log set is covered in soot, however, this is not a normal condition and a fireplace professional should be consulted. The vent-free log set may not be operating properly if there is a heavy soot layer present. Normal soot can be gently brushed away with a paint brush if desired. Do not remove the log set from the fireplace or use water or abrasive cleaners.