Boiled VS Raw Linseed oil
This is a question that I have been pondering about for quite some time, and that I have found to be quite a hot-topic on other internet forums and by stockers I spoke to.
My findings start with the quality of the oil regardless of it being boiled or raw.
At he beginning I was not that peculiar of what oil I used. I just went to the hard wear store and picked up whatever that was in the shelf. Nowadays I am more picky with what I choose. Today I only buy high quality cold pressed linseed oil from artist stores and such since I have found that the quality is superior of the cheap stuff. Mostly due to less crap that what You get in the cheaper bulk products.
After some reading up and contacts with producers of linseed oil and practical applications I have come to the following conclusions.
Raw:
Better penetration into wood since the molecular size is 100 times smaller than in Boiled Linseed oil- ca: 0,000005 0,000001mm = 5 -1 nm. The low viscosities allow the oil penetrate deep into the wood- hence giving it a deeper finish?
Drying/hardening/polymerization is very long without additives and therefore You need driers like turpentine or other additives to stabilize it. I have found that if You use pure raw oil, the wood can start too bleed after You applied it-specially in high temperatures. Not very good if You want a stable finish.
Polymerization-letting the molecules bind together in larger clusters (hence making them more stable?) seems to be a key part to getting a stable finish that wont bleed out of the pores in the wood. I have also seen comments about the raw oil that it can accumulate growth of mold and bacteria due to that it is containing proteins, fat and amino acids, and that is one of the reasons that you put additives into it and heating it up. I will check into this part a bit closer.
There is also whats labelled as oxidized raw linseed oil. This is made by putting raw linseed oil into open air containers which is submitted to sunlight an oxidization for about 6 months. I have not tried this type of oil yet, but its said to have better drying/hardening/polymerization capabilities than Raw linseed oil. I was informed that the process changes the molecular size towards Boiled linseed oil. It is also extremely expensive.
Boiled, which seems to be oil with addition of different chemicals rather than boiled or heated in many cases. High quality oil although seems to actually have been heated/boiled.
Larger molecular size than raw oil 0,0001 mm = 100 nm. It extends to about 15% when it dries and clogs therefore well inside the wood. The linseed oil oxidizes rapidly over low heat development or addition of driers. The drying/hardening time is one or two days in comparison to raw oil which might take weeks or months
So here is the first divider- what shall You use as a base for Your Slacum or Red oil?
You want penetration I assume. But how much do you really need?
Raw oil to get the penetration and depth -with some additives to speed up the hardening- or Boiled linseed oil with the benefits of quicker hardening?
Do You really benefit from the deep penetration capabilities of the raw oil or will boiled oil suffice for the grain structure of walnut? The pores in wood is about 0,03 mm.
Both? Start up with raw oil-and additives-and then move over to boiled-and additives?
Mixing them together to get at two-in one combined with driers/ additives?
Do the additives change the penetration capabilities of raw linseed oil- do they by aiding the polymerization process increase the molecular structure of the oil and therefore have a negative impact on penetration?
What is Your experience in this field- if You want to share what are Your standpoint regarding raw vs boiled linseed oil?
I have found out that different pieces of wood -I have mainly been working witch European-French walnut- react differently to raw linseed oil and Boiled linseed oil. Usually the really dense and hard stocks need to have some raw oil into the Slacum to get a deep penetration into the grain structure.
