# BLO turning black with age?



## Kevin07 (Feb 19, 2009)

I was doing some reading today and came across a post on a diffrent forum and they were talking about BLO and how it will turn black over a long period of time.:thumbdown: Some people were saying that even the "boiled" linseed oil will not fully dry, it will get a film but not dry under that. So using BLO on almost all my cherry projects should i stop? This is a new to me.


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## robbiethewood (Jan 15, 2012)

hi i don't use it not because i don't like it
but i can tell you Richard raffan swears by it he has being using it for years
check out his site http://www.richardraffan.com/


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## chemmy (Dec 13, 2011)

Kevin07 said:


> I was doing some reading today and came across a post on a different forum and they were talking about BLO and how it will turn black over a long period of time.:thumbdown: Some people were saying that even the "boiled" linseed oil will not fully dry, it will get a film but not dry under that. So using BLO on almost all my cherry projects should i stop? This is a new to me.


I guess that depends on what the poster was suggesting or implying when making that statement. If he meant it would turn "black" when used as a finishing oil on wood, then no i personally have never read, studied, or heard of that taking place chemically or otherwise. If he meant it could be heated and cooked to the degree that it would turn black, as any other oil, then yes that is true. Having seen very early samples of linseed on antique furnishings, it can get very dark and if a lot of grime from smoke or other dark substances had been rubbed in over the centuries old finishes they may appear that dark to some, but with good cleaning with solvents or other conservative soaps etc. much of that darkness can be removed. 

Oils, especially those not polymerized and or treated with siccatives[ dryers] can take a very long time to "cure" Depending on the amount of refining the oil initially goes through and can have varied affects on the drying properties. Ones that are normally acid or alkali refined, bleached and then polymerized and have both a top dryer and through dryer added will and do dry to cure much faster than ones that are nor processed in this manner. 

Personally i think you would be better of with polymerized tung oil which does not continue darkening over time once it reaches it's darkest point which is fairly soon, but i will leave you to decide on that. Meanwhile, i would not be overly concerned with linseeds darkning for it will not get that dark that quickly in your lifetime, unless you may be only 6 years old.


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## Murphy's Law (Dec 15, 2011)

I use BLO on all of my wooden handles on shovels, rakes, axes, etc. to help keep them in good shape. They get darker as with almost any oil application but so far they have not turned black. Two years ago I used the BLO on some new small bird houses made of junk pine and just today I pulled them out of the barn to get ready to put them out. Six of seven birdhouses are almost black and the other one is very dark. So maybe the darkening is caused by exposure to sunlight or the weather.


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## chemmy (Dec 13, 2011)

Murphy's Law said:


> I use BLO on all of my wooden handles on shovels, rakes, axes, etc. to help keep them in good shape. They get darker as with almost any oil application but so far they have not turned black. Two years ago I used the BLO on some new small bird houses made of junk pine and just today I pulled them out of the barn to get ready to put them out. Six of seven birdhouses are almost black and the other one is very dark. So maybe the darkening is caused by exposure to sunlight or the weather.


hmmm? post pics please, never mind i just read up on it, caused by peroxide destrucion by UV, this is why only exterior exposed linseeds would be greatly affected and not interior woodwork or furniture. Good to know thank for the post.


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## Carlo Bartolini (Aug 30, 2011)

Murphy's Law said:


> I use BLO on all of my wooden handles on shovels, rakes, axes, etc. to help keep them in good shape. They get darker as with almost any oil application but so far they have not turned black. Two years ago I used the BLO on some new small bird houses made of junk pine and just today I pulled them out of the barn to get ready to put them out. Six of seven birdhouses are almost black and the other one is very dark. So maybe the darkening is caused by exposure to sunlight or the weather.


It's common for sailors to oil exterior wood, in tropical rainy climates it turns dark almost black, it collects dirt, from rain specially, the first 15 minutes of rain is quite dirty, and perhaps bacteria. On the spots on the boat where rain does not fall, the oil looks nicer for much longer.

Peroxide destruction by UV....interesting....

I have never seen a finish that can handle the elements....best I've seen is well sanded ipê (tabebuia)...and left to turn gray.....unfinished....


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## cabinetman (Jul 5, 2007)

Kevin07 said:


> I was doing some reading today and came across a post on a diffrent forum and they were talking about BLO and how it will turn black over a long period of time.:thumbdown: Some people were saying that even the "boiled" linseed oil will not fully dry, it will get a film but not dry under that. So using BLO on almost all my cherry projects should i stop? This is a new to me.


I'm not surprised about what you can find on forums. It's mind boggling. I haven't seen interior finishing done with BLO or pure Tung oil turn black. Some of those pieces are 30 years old already. 

The statements about darkening may be attributed to wood that darkens with an oil finish, versus the oil getting dark or black.










 







.


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## Carlo Bartolini (Aug 30, 2011)

The blackening of the oils (linseed, tung, teak oil - a mix) in exterior is inevitable, tung takes the longest to blacken, so I did a test about 6 months ago. On white 2k paint.

This is cold pressed polymerized Tung Oil from Paraguay (lighter colored and less darkening than Chinese, color gardner = 7, RI 1.52).

I am not an experienced finisher as cabinetman, but from what I know...he is correct....metallic driers do increase darkening...but not blackening, as far as I know...


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## HowardAcheson (Nov 25, 2011)

>>>> how it will turn black over a long period of time.

Yes, that's true. That's the reason most antique items are dark brown or black. It takes maybe 150 to 200 years for it to occur. Makes no difference whether is it "boiled" linseed oil or raw linseed oil. It's the natural result of the oxidation of the oil.

I talked with a couple of the curators at the Williamsburg restoration and they said that they had to formulate a finish to mimicked the real old finish on some of their older items.


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## Carlo Bartolini (Aug 30, 2011)

I find this all very interesting, Cabinetman, does your linseed stuff keeps on darkening? Has it become a lot more transparent? - it is known that linseed after a few years becomes more transparent.

Howard, did they say darkening or actually cases of blackening?

Did a quick research and found a picture of a german Roth violin fro 1926, Roth supposedly applied very dilute linseed to the bare wood. (althoughI don't know if he did that on this specific violin)


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## chemmy (Dec 13, 2011)

Carlo Bartolini said:


> The blackening of the oils (linseed, tung, teak oil - a mix) in exterior is inevitable, tung takes the longest to blacken, so I did a test about 6 months ago. On white 2k paint.
> 
> This is cold pressed polymerized Tung Oil from Paraguay (lighter colored and less darkening than Chinese, color gardner = 7, RI 1.52).
> 
> I am not an experienced finisher as cabinetman, but from what I know...he is correct....metallic driers do increase darkening...but not blackening, as far as I know...


Carlo i have contacted both ADM [ Archer Daniels Miland] oil and the oil division of Cargill the only two manufacturers of oil here and neither have ever heard of linseed oils be they natural or boiled going black in any reports of that which they make or have sold over there lifetimes in business. Yellowing, darkning, yes, but not turning black. The only person that would be able to give me more indepth info on this subject is not available at this time, though i will try to continue to contact him in the future, it takes an organic chemist [not] my feild] who has studied the affects of UV on these oils to give me what i know. Most, unless in the feild of natural oils would not be of help. Though they could be if they wanted to look at the suject and find the causes. Maybe your oil sources there could be of such help if you desire to look into it further. if so report back as to the authenticity of what i have dompiled so far as to the affects of UV's on the hydro peroxides having this affect on the oil ok?

Secondly, although i do see black particulation in the oil, in your pic, i donot see the entireity of the oil being black, as if something is happening within the oil and not directly to the overall make up itself agreed? This however, is doubtful of the action being of or from driers that are most oft used in the boiled oils. If this had been a common problem or concern from a hundred or more years of use, of either the oils themseves or driers then it would have benn addreseed by those who manufacture the products along time ago.

Along with this is also the possibiltiy of molds that may have gotten into the lessrefined oils of commerce since there are black molds. I cannot see however it happening to the more reined oils. S o many people get there oils from the dregs that are sold at big box stores, one can never know for sure how clean they are as to refining. the highly refined ones should never have this problem, though the hydroperoxides are a distinct issue that i still cannot fully address as of now.


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## Carlo Bartolini (Aug 30, 2011)

Great Chemmy...thanks for the info.....I was really curious as to the darkebing effects of linseed, as to how dark it can get and if the blackening was actually possible to happen indoors, as you point out, no blackening possible indoors.

I also did a bit of research on Maestronet, as the violin makers think inthe hundreds of years and have records of what some of them have been doing for quite a while.....could not find anything about blackness that is kown t e linseed...only as you mentioned, yellowing and some darkness.... but if that Roth violin has indeed a linseed ground, than the darkening probably stops after a certain time?

Also, many of them mention the fact that it becomes more transparent with time.

Also cracking of the film etc...

Mine Polymerized Tung oil, that has become black is because of dirt, mostly from rain, I have spoken to the chemist who polymerizes it a while back, asked if it was dirt and he said "yes" - - My thinking is -- as the oil is somewhat hygroscopic it absorbs dirt with the water, as I've mentioned above, the first 15 to 20 minutes of rain contain lots of dirt, an I'm in rain forest, good place to see that.....

I have tried in my unfinished exterior wood, all kind's of oils, they all blacken, for the reason above, in about 5 to 6 months, if constant maintenance is done, it can last longer.....but eventually will go black...tat is why I did that test, so I would know for sure....

Raw linseed blackens faster - my thinking is that because it takes longer to dry it receives rain before it's dry....the rest you know..

Once again thanks for the precise info.


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## Midlandbob (Sep 5, 2011)

I think you'll find that the serious issue of BLO going black is outside applications and particularly damper locations. I think it it attributed to final growth in the oil finish.
Oils and the wood do continue to darken over time. Lots of the beautiful grain we love will transform to a uniform dark colour over many years.


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## Midlandbob (Sep 5, 2011)

Sorry. That was fungal not final. I accidentally hit the send button.


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## chemmy (Dec 13, 2011)

Midlandbob said:


> I think you'll find that the serious issue of BLO going black is outside applications and particularly damper locations. I think it it attributed to final growth in the oil finish.
> Oils and the wood do continue to darken over time. Lots of the beautiful grain we love will transform to a uniform dark colour over many years.


Your right Bob, unless the oil is highly purefied there can be both mildew or mold that can grow especially outdoors, but unless it is a black mold like in florida it would not turn black in a year as the bird houses did. still searching for answers from my chemsit friends on this, maybe i'll get lucky, maybe not.


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## Midlandbob (Sep 5, 2011)

The " black" mold is everywhere. The black lines in spalting etc. Wood can go black is short order. Fresh cut maple and some other woods can go black in days if not well stickered and the surface dried to inhibit the mold.
Mold spores are everywhere. Mildew is is largely the fungal spores on the surface of wood, leaves etc.. Several mold species grow on the surface of plants and have structures that form millions of spores. It is often apparent as a fuzzy white or black patches that gets called mildew.
A cedar shed I finished with an linseed oil based finish turned black close to the damp ground and worse in the shady places.
Fungi grow very fast in the suitable conditions. BLO is like a salad oil film to the molds.


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