Here's a follow-up to the first article.
I do have a related question. What is boiled linseed oil and how does it compare to 'regular' linseed oil. Also, I am building a children's picnic table out of pine or cedar. I have been told to finish it in linseed oil, but don't know if it should be boiled linseed oil or not or what the technique is. Any thoughts?
Where does polymerized tung oil fit into the story? I know it is "heat bodied" but does this process get a jump on the polymerization?
I hope this does not put you to sleep... Both nonconjugated and conjugated drying oils can be polymerized by heating under an inert atmosphere. These polymerized oils are then referred to as "Bodied Oils". To achieve the higher viscosity's of bodied oils, nonconjugated oils are heated up to 320 degrees Centigrade and conjugated oils are heated up to 240 degrees Centigrade.
The increase in viscosity or "body" is caused from thermal decomposition of naturally occurring hydroperoxides. This decomposition yields free radicals that contribute to a limited amount of cross-linking. The heating of Tung Oil must be carefully monitored or the polymerization will lead to gelation of the oil. The viscosity can also be increased by passing air through the oil (Blown Oils) at high temperatures (up to 150 degrees Centigrade). Reactions similar to those observed in cross-linking cause oligomerization of the oil.
To put it into simpler terms...
Pure Tung Oil cures through polymerization and oxidation. To speed the drying process further, manufacturer's heat the Tung Oil (now called Polymerized Tung Oil) which completes polymerization portion of the drying process. This speeds the drying time, because half of the process has already been completed. Polymerized Tung Oil (PTO's) when applied, cures through oxidation and evaporation of any solvents.
Polymerized Tung Oils dry faster, harder and are more durable than "pure" Tung oils. In addition PTO's produce a smooth glossy finish, whereas Pure Tung Oils produce a matte sheen due to the expansion that takes place during polymerization. This expansion creates a very finely textured surface, that appears to the naked eye as a matte finish.
Some specialized Polymerized Tung oils are processed at very high pressures and temperatures. These are called "Thermalized Tung Oils" (TTO's) and are used in nitro-cellulose lacquers.
Linseed Oil is obtained from Linseed or Flax (Linum usitatissimum). It is obtained by various methods including pre-expelling, followed by hexane extraction of the press cake. The resultant oil is refined to remove phosphatides and gums, which naturally occur in the oil. (Post-desliming with sulfuric acid and phosphoric acid, yields oils with virtually no traces of phosphatides or gums).
Further post-treatments include lye neutralization and earth bleaching, which yield very light drying oils. The natural odour of Linseed oil is removed through a deodorization process (if desired), as a final step in the refining process.
Therefore, "Raw Linseed Oil" (RLO) is simply, Linseed oil that has been extracted and packaged without any additional additives. Raw Linseed Oil takes significantly longer to dry than "Boiled Linseed Oil" (BLO) (RLO-needs a few weeks to cure, vs 36-48 hours for BLO to cure).
So called "Boiled Linseed Oil" is Linseed Oil that has been altered through the addition of chemical drying accelerators, i.e. solvents and siccatives/driers. BLO is frequently mixed with 10-15% Stand Oil (SO's). SO's are drying oils of increased viscosity, which is achieved through heating the oil in the absence of oxygen.
Traditionally, driers contained combinations of oil-soluable metal salts like cobalt and/or manganese with zirconium, lead or calcium salts of 2-ethylhexanoic acid or naphtenic acids. Cobalt and maganese salts act as "surface driers" and aid in the drying of the film on the surface, where oxygen concentrations are the highest.
Lead and Zirconium salts catalyse throughout the film and are known as "through driers". Calcium salts help to reduce the amounts of other driers that may be needed. Various other compounds may also be present in some BLO's including but not limited to: Beryllium, Cadmium and Nickel.
As for whether or not you should use any Linseed Oil for a preservative on an exterior children's picnic table... That really depends on what you prefer. There are many exterior finishes that will outperform both raw and boiled Linseed Oil. Other negative factors to consider when considering Linseed Oils for exterior applications (boiled or raw) include:
I do have a related question. What is boiled linseed oil and how does it compare to 'regular' linseed oil. Also, I am building a children's picnic table out of pine or cedar. I have been told to finish it in linseed oil, but don't know if it should be boiled linseed oil or not or what the technique is. Any thoughts?
Where does polymerized tung oil fit into the story? I know it is "heat bodied" but does this process get a jump on the polymerization?
I hope this does not put you to sleep... Both nonconjugated and conjugated drying oils can be polymerized by heating under an inert atmosphere. These polymerized oils are then referred to as "Bodied Oils". To achieve the higher viscosity's of bodied oils, nonconjugated oils are heated up to 320 degrees Centigrade and conjugated oils are heated up to 240 degrees Centigrade.
The increase in viscosity or "body" is caused from thermal decomposition of naturally occurring hydroperoxides. This decomposition yields free radicals that contribute to a limited amount of cross-linking. The heating of Tung Oil must be carefully monitored or the polymerization will lead to gelation of the oil. The viscosity can also be increased by passing air through the oil (Blown Oils) at high temperatures (up to 150 degrees Centigrade). Reactions similar to those observed in cross-linking cause oligomerization of the oil.
To put it into simpler terms...
Pure Tung Oil cures through polymerization and oxidation. To speed the drying process further, manufacturer's heat the Tung Oil (now called Polymerized Tung Oil) which completes polymerization portion of the drying process. This speeds the drying time, because half of the process has already been completed. Polymerized Tung Oil (PTO's) when applied, cures through oxidation and evaporation of any solvents.
Polymerized Tung Oils dry faster, harder and are more durable than "pure" Tung oils. In addition PTO's produce a smooth glossy finish, whereas Pure Tung Oils produce a matte sheen due to the expansion that takes place during polymerization. This expansion creates a very finely textured surface, that appears to the naked eye as a matte finish.
Some specialized Polymerized Tung oils are processed at very high pressures and temperatures. These are called "Thermalized Tung Oils" (TTO's) and are used in nitro-cellulose lacquers.
Linseed Oil is obtained from Linseed or Flax (Linum usitatissimum). It is obtained by various methods including pre-expelling, followed by hexane extraction of the press cake. The resultant oil is refined to remove phosphatides and gums, which naturally occur in the oil. (Post-desliming with sulfuric acid and phosphoric acid, yields oils with virtually no traces of phosphatides or gums).
Further post-treatments include lye neutralization and earth bleaching, which yield very light drying oils. The natural odour of Linseed oil is removed through a deodorization process (if desired), as a final step in the refining process.
Therefore, "Raw Linseed Oil" (RLO) is simply, Linseed oil that has been extracted and packaged without any additional additives. Raw Linseed Oil takes significantly longer to dry than "Boiled Linseed Oil" (BLO) (RLO-needs a few weeks to cure, vs 36-48 hours for BLO to cure).
So called "Boiled Linseed Oil" is Linseed Oil that has been altered through the addition of chemical drying accelerators, i.e. solvents and siccatives/driers. BLO is frequently mixed with 10-15% Stand Oil (SO's). SO's are drying oils of increased viscosity, which is achieved through heating the oil in the absence of oxygen.
Traditionally, driers contained combinations of oil-soluable metal salts like cobalt and/or manganese with zirconium, lead or calcium salts of 2-ethylhexanoic acid or naphtenic acids. Cobalt and maganese salts act as "surface driers" and aid in the drying of the film on the surface, where oxygen concentrations are the highest.
Lead and Zirconium salts catalyse throughout the film and are known as "through driers". Calcium salts help to reduce the amounts of other driers that may be needed. Various other compounds may also be present in some BLO's including but not limited to: Beryllium, Cadmium and Nickel.
As for whether or not you should use any Linseed Oil for a preservative on an exterior children's picnic table... That really depends on what you prefer. There are many exterior finishes that will outperform both raw and boiled Linseed Oil. Other negative factors to consider when considering Linseed Oils for exterior applications (boiled or raw) include:
- Lack of any UV inhibitors.
- On surfaces where abrasion will be frequently encountered, Linseed Oil may not harden sufficiently, causing frequent repair.
- Linseed Oil can support the growth of mildew.
