I have a 10 year old log home .the logs are white pine . The interior logs were covered with clear sikkens finish as recommended by log manufacturer when constructed. The logs look great but the knotty pine areas are darkening . A lot of the knots now look black . None of the flat white pine is discolored- only the knotty areas of the logs. Is this a normal color change over time and should this be expected . It appears to be a uniform change thru out the house which is all logs. Thank you for