Boiled linseed oil, often written as BLO, is not as it sounds– there’s no heating or boiling involved (unlike polymerized linseed oil).
The difference between raw linseed oil and boiled linseed oil is that there are siccatives (metal or petroleum-based drying agents) added to BLO to shorten the time it takes for the oil to cure. This shortened drying time makes boiled linseed oil a more practical finish for woodworking, as raw linseed oil can take weeks or months to fully cure.
Some of the petroleum-based siccative compounds that are added to linseed oil to decrease the drying time are naptha, mineral spirits, and dipropylene glycol monomethyl. Cobalt and manganese are the most common metal siccatives found in boiled linseed oil.
Boiled linseed oils often carry the following warning as required by the state of California:
“Warning: This product contains a chemical known to cause cancer and birth defects or other reproductive harm.”
Note: If you’re buying furniture with a boiled linseed oil finish, we highly recommend you check with the craftsman to better understand the composition of the oil. Ask for the brand of the finish used and skim through the MSDS spec sheet to see what sort of chemicals and warnings are associated with the use.
Learn more about linseed oil and how to apply it to furniture safely.