What Is Linseed Oil?

Linseed Oil is used in wood finishing which has been around for generations. It is made from the seeds of the flax plant and comes in a couple different options from pure oil, polymerized, and what is called Boiled Linseed Oil.

If you need the safety data sheet for this oil the link provided gives data for both raw and boiled versions.

I have the strong opinion that this oil should not be used in wood finishing as it has within previous generations. That may come as a shock to woodworkers out there, but it is merely my opinion. Why? Let’s dig into more of what this oil is and what other better options exist.

Problems With Linseed Oil

My biggest complaint with Linseed Oil is how it will yellow over time. This is especially seen in wood such as Maple. It is not a natural wood patina but rather the oil itself. The variant of the oil which you use does not matter as this effect still will come with age.

Let’s focus on two other issues. Boiled Linseed Oil is not true to its name as it is not boiled at all. Rather other chemicals are added to aid in drying time. With this specific product I have one major issue with this and another minor one.

The minor issue is that BLO has been known to self combust. Really it is not that big of a problem as long as you do not wad up a rag and throw it in a trash bin with tinder. Just use common sense.

The major issue I have is that I feel these chemicals do not allow enough time for the oil to penetrate the wood as it should. I know this can be argued. Yet it is how I personally feel about the product and never use in in my wood art.

Raw Linseed Oil on the other hand can take a lifetime to dry. Okay, in reality about 2 to 10 weeks drying time. The polymerized version is the best between those two worlds in my opinion. It drys faster than raw oil but not as fast as BLO.

Know that the boiled version of this oil is not food safe. Raw Linseed Oil is food safe. There has been argument by some in how it is used and whether or not it can go rancid. This argument I will go into more soon yet depends upon common sense use.

My Argument On Boiled Linseed Oil Penetration In Wood

When oil of any kind is applied to wood in order for it to protect the wood it needs saturation and penetration. This is about wood fibers and how well it seals not merely the surface but also the outer layers of the wood.

Oil is not like a polyurethane. Polyurethane predominantly sits on top of the surface creating a barrier to prevent things such as moisture from penetrating. Oil on the other hand soaks into the fibers of the wood itself and exposure to oxygen causes this polymerizing “drying” .

When I have used BLO on wood surfaces there are inconsistencies which I have seen across time in the wood. Additionally there are inconsistencies which I have felt in my hands. We always apply more oil to get the even finish we desire and all is well.

Yet when using other products such as Tung oil, I see and feel that it is a better finish which is more consistent across the surface. I have simply come to believe that these additional agents added to BLO seem to sometimes short circuit what Raw Linseed Oil and Tung Oil does a better job at doing.

Why Not Use Polymerized Linseed Oil

First know that not all polymerized oils are equal. There are products you can find called “true polymerized” which have no additives. So allow me to explain what the difference is.

To polymerize Linseed Oil they take the oil and heat it but deprive it of oxygen. Over the course of a few days it polymerizes and this aids in reducing drying time. Yet this “true version” of the polymerized oil still drys slowly.

So here is the rub to make you scratch your head. Polymerized Linseed Oil is technically “boiled” as it is heated to around 572 degrees Fahrenheit in order for it to polymerize. Yet Boiled Linseed Oil (BLO) which is not “true” has the additives for drying and is not food safe.

Without additives it can be difficult to get the drying time down to a couple of days. I will say that if you wish to use Linseed Oil this true polymerized version without additives is the best option.

This though cannot compare to Tung oil which is food safe, does not yellow with time, and also dries inside of three days.

Will Linseed Oil Go Rancid?

Here is the argument that can make some go mad trying to figure out. Wikipedia for example will tell you that it does go rancid. I will help this make sense quickly.

Within the context of what Wikipedia is explaining, it is speaking to pure cold pressed oil and its use in nutritional value as well as its storage. It states it can go rancid unless refrigerated. Well, we are not refrigerating our wood.

Within the right environment pure Linseed Oil will not go rancid.

Why? It is a drying oil. So what is the problem? The time it can take to dry. When it is applied in its pure form it is thick and does not apply easily. The first rule is, do not apply leaving a thick layer on the wood.

The problem can come from outside contamination. If you apply the oil in thick layers and set it on a shelf then forget about it then issues may occur. It helps to have air circulation and heat to aid in drying.

This also helps prevent any potential nasty things from developing. The oil itself is not a problem when applied properly.

Nevertheless this whole argument is another reason why I love Tung oil. In its natural form it is great, food safe, and it just dries. Less hassle and no worries involved.

When it comes to Boiled Linseed Oil you have nothing to worry about. Just store it properly and apply. Just keep in mind it is not food safe by the very nature of the additives which are added to begin with.

What Makes An Oil Go Rancid?

Quite simply the answer is whether or not it dries on the surface of what it is applied to. The longer it takes to dry, or polymerize, the more likely it is to potentially go rancid.

Thus this reason is why there is some confusion about pure Linseed Oil. Due to the length of time it takes to dry the conditions surrounding the piece can matter. Personally I would never use this oil on a cutting board, yet that it is me.

Never Use Linseed Oil On Painted Artwork

Believe it or not there are artists who have attempted to use Linseed Oil on their artwork. Yes you read that properly. This is not a good idea.

Artists have used drying oils of different kinds for ages. Often its purpose serves to aid in protecting the artwork. While Linseed Oil will dry, it is a conditional thing.

Within wood the oil seeps into the fibers as they absorb them. Its drying is the polymerizing of the oil which is done with exposure to oxygen. The idea of using this oil on a painting is in no way the same thing.

If you attempt to use this oil on artwork then you will find it seems to sit forever on the surface and never dry. It does not evaporate. Rather you have an oily surface that will eventually form a slight crusty feel.

It is true that some paints have this oil as an additive. Yet this is a very different thing than using the oil as a protective coating itself.

Overall View Of Linseed Oil

In truth Linseed Oil is not a bad thing at all. It has been around forever and has been used in various ways across generations. Even within cutting boards it is not the worst option, just not my preferred as Pure Tung Oil is far better.

Why do people love linseed then? It does give a rich finish to wood. This is especially true of many hardwoods where a variety of color can be found.

When Linseed Oil is added to the wood it will darken it. It will have that nostalgic appearance that we have come to love.

There is nothing wrong with using this oil as long as you understand what you are using and what its purpose is for. The biggest issue I see comes from confusion which people have from the different versions found on the market.

Just keep in mind to never use Boiled Linseed Oil on something that needs to be food safe and you will be fine. The rest really comes down to personal preference, experience, and desires you have for the project.

If you have twenty years (exaggeration here) to wait for the pure version to dry and that is your preference then go for it. There is nothing wrong with using the oil.

Pure Linseed Oil:

It is cold pressed to obtain the oil from flax seeds. It does not receive any heat treatment nor will there be any additives present.

It is a drying oil. Yet it does require two to ten weeks for wood to dry after application. Apply in thin layers.

Rarely will it ever go rancid in typical and practical uses. Shelf life may vary yet often suggested is approximately 6 months. Personally I have known woodworkers to have this oil sitting around for much longer with no issues as a result. Your mileage here may vary.

Polymerized Linseed Oil:

This is pure Linseed Oil which has been heat treated yet deprived of oxygen in the treatment process. No additives can be found within the product. Its drying time is decreased yet still not as fast as Tung Oil.

This version is food safe IF it has no additional compounds added. The problem here can at times be finding this version being sold.

Boiled Linseed Oil or BLO:

This version of Linseed Oil is NOT the same as Polymerized. BLO has had additives placed within the oil to speed drying time. Typically this version of the oil will dry within a day to a few days depending upon application.

It is not food safe and should never be used on items such as cutting boards or serving trays.

Linseed Oil Compared To Mineral Oil

I add this here for questions I have often found within forums from newer woodworkers. The question comes in asking which of these two is better.

The answer is it really depends on your preference as long as you know what they both do. The biggest difference is that Mineral Oil needs to be reapplied after every washing of the wood item.

In my opinion Linseed Oil is better for the longevity of the wood item at hand. The goal of any oil is to prevent moisture of various kinds which can cause problems or contamination in the wood from getting there.

Due to the ability of water to remove Mineral Oil from the wood in washing it provides an opportunity for contamination. This is why between these two options I would choose Linseed Oil over Mineral.

The Best Option For Oils In Wood

If you cannot tell my favorite wood oil already then you will know now. My favorite is Pure Tung Oil. Yes it does have its issues such as being thick in this form, yet all pure oils typically do.

Yet it applies well, dries within days, and is food safe. All around it is difficult to beat. In my opinion Tung Oil is preferred over Linseed Oil especially within applications where food preparation is required.

While Linseed Oil is safe, it can take a week or more to fully dry. It is a matter of not having to wait for the wood item to be used any longer than one must. No one wants residual oil seeping into their food after a cutting board has had a new application of oil.