By all reports starting with the MSDS and researching forward. Trade secret stuff but it acts like spar varnish mixed with drying oil and Japan dryers though some would say poly varnish. A mixture that had been around before Newell wrote his book. BTW, all BLO is low grade linseed? Where does the high grade stuff go, cheap barn paint? Depends on where you get it. Speaking of Newell he was no fan of paint store linseed. Writes you don't know how long it's been on the shelf. Wrote the stuff begins to degrade after 6 months IIRC.
