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brushmarx
12-03-2005, 10:33 AM
Hi! Was wondering if linseed oil was toxic. Also,inregards to M Grahams' walnut oil and mediums: the bottle on the walnut oil medium says it dries faster, what does the bottle that says walnut oil do? Why do you like to use it? Is it toxic?
Thank you all! maria:rolleyes:

aszurblue
12-03-2005, 11:07 AM
I can tell you that "for me" one drop of linseed oil on my skin and I'll be sick for up to three days:( So have to wear gloves and be very very careful when using oils. I haven't tried the Walnut Oil yet, but would be interested in others views on this. Azure

rroberts
12-03-2005, 02:11 PM
Raw linseed oil is practically non-toxic. It has historically been used as a laxative. It is well absorbed through biological membranes such as the stomach and skin. Linseed oil can be irritating to the skin and is known to contain potent allergens. Cautions against the use of boiled linseed oil are common in health literature due to toxicological concerns about its additives. Thermopolymerized linseed oil (heated to high temperatures) may be toxic to the liver.
(http://www.greenconsumer.cc)

Walnut Oil, on the other hand, is a widely used food item, but a percentage of the population have allergic reactions to some or all nuts and nut products.

NOTE! If you have health concerns about your personal experience with either of these oils, you should consult your physician.

Walnut oil drys somewhat differently than linseed, sometimes a bit faster. M. Graham's claims about faster drying might lead you to believe there's a significant difference between the two. M. Graham walnut alkyd medium, though, probably does dry faster, but it is an alkyd, therefore a quite different critter from regular walnut oil.

cheers!

Calvado
12-03-2005, 03:58 PM
When I'm in shortage of olive oil, I use it (linseed oil) in my salads as a dressing.

turlogh
12-03-2005, 05:39 PM
You can buy both linseed and walnut oil in health food stores (the linseed is labelled "flax seed oil"). The stuff used for paint is processed differently, but essentially the same. They are natural and non-toxic.

dbclemons
12-03-2005, 05:59 PM
I understand the processing of linseed oil for painting involves adding metallic dryers which might make it somewhat toxic. Raw linseed/flax oil as a food oil is not recommended as a cooking oil but has the health benefit of omega-3 fatty acid as found in fish.

-DBC

gunzorro
12-03-2005, 06:15 PM
Metallic driers aren't used to process Linseed so far as I know.
It is edible and completely safe, except for slight risk of possible allergies or psychosomatic reactions. Jim

Calvado
12-03-2005, 06:23 PM
As I said, try it in your salad... delicious :) lololol

Einion
12-04-2005, 05:35 AM
I understand the processing of linseed oil for painting involves adding metallic dryers which might make it somewhat toxic.Nope, not in the standard types.

"Boiled linseed oil" that you'd see in a hardware store will sometimes contain metallic driers though. These driers, if present, would tend to be highly toxic - cobalt and manganese are often used - but they'll come with appropriate health warnings if they do.

Einion

dbclemons
12-04-2005, 11:33 AM
http://en.wikipedia.org/wiki/Linseed_oil
"Boiled linseed oil was used as a paint binder or as a wood finish on its own. ... However, today, metallic dryers are used instead of heat. The use of metallic dryers makes boiled linseed oil inedible."

Maybe it's just not always the case. Art supplies aren't always good about detailed labeling as for food or hardware products, to a lesser degree. There's a bottle on a grocery store shelf up the street from me that says "100% pure linseed oil" and nothing else on the label. If it's something that might be a health risk, it would be wise to try and contact the manufacturer to get more info.

-DBC

turlogh
12-04-2005, 11:52 AM
I don't recommend eating linseed or walnut oil sold for use in painting. If I happened to accidentally ingest a small amount, I wouldn't worry unless it was specifcally labelled as containing driers or other toxic substances.

gunzorro
12-04-2005, 02:33 PM
Any reputable art materials maker is not going to add something toxic without telling the buyers! You won't find any quality artist linseed products with driers or toxic additives. I don't know why this is not sinking in.
Are you worried there is a conspiracy here? :) Jim

LGHumphrey
12-04-2005, 03:52 PM
So is it OK to use the flax-seed oil from a health food shop for painting?

rroberts
12-04-2005, 05:01 PM
So is it OK to use the flax-seed oil from a health food shop for painting?

That's a good question! I don't know. However, I hesitate to recommend health-food store flax oil for painting. I bet Einion and/or Turlogh probably have more specific info on this.

For your own satisfaction, though, why not do a little test?
On a piece of glass (or similar non-absorbent surface), paint a patch of both oils. Let them dry, expose them to sun, let them sit around for a while. Then examine the film and see if one is stronger than the other, or a different color. In fact, for a more thorough test, make patches of oil alone and oil with pigment.

I recall reading somewhere that there are actually two kinds of flax produced, one specifically for the paint industry. However, I don't know if that's true, and wouldn't be able to find the reference at this point.

cheers!

tk04
12-04-2005, 07:03 PM
The largest "problem" with artist's linseed is probably that it's self-combustible. I know about fires caused by it. A rag with linseed can start burning without any specific fire-source, like a match or some other open fire. So it's important to have a safe procedure for disposal of rags, and alike.

If you buy linseed oil, or walnut, in a food-store you wouldn't know how weel-refined it is, or the general quality of it. Artist's linseed oil doesn't cost much if you buy a larger amount of it, so it's not much to gain on buying it in food-stores.

Common sense says that one shouldn't put artist's linseed oil in food - for the same reasons - the producers aren't making them for food, but for painting, so it may contain "something", even if it normally won't.

Some people may be allergic to linseed oil. As for that, if you get too much exposed to for instance normal detergents, you can develop allergies gradually. That's not uncommon among people that make a living from washing. Nut-allergies are known to be outright dangerous.

Einion
12-05-2005, 04:34 AM
If you buy linseed oil, or walnut, in a food-store you wouldn't know how weel-refined it is, or the general quality of it. LOL, one doesn't know this about the artists' types either :D

Einion

tk04
12-05-2005, 09:25 AM
If you buy linseed oil, or walnut, in a food-store you wouldn't know how weel-refined it is, or the general quality of it.

LOL, one doesn't know this about the artists' types either :D

Einion

No, striktly speaking, that's true.

But you don't need to be a genius to find info about this in of the many books on artist's materials. I quote from Ray Smith: "The oil is pressed from seeds. Modern oils are normally hotpressed. One can also buy coldpressed oil, which is considered as being of better quality." (my translation from Norwegian - the book itself is originally english).

Leonardo complained about his contemoraries not processing their oil properly, according to a book I have read at some time. I'm sure he would have been happy with the present situation. Now, even amateurs or sunday painters can buy artist's oil processed in factories, or where-ever they make it, probably of better quality that the one used by Leonardo himself.

So, if you buy artist's oil you know it's processed for artistical use. Since artistical oil isn't that expensive, I don't see the point in using food-store oil in painting mediums even if they sell drying-oils in food-stores.

Andrew
12-05-2005, 12:44 PM
You can buy both linseed and walnut oil in health food stores (the linseed is labelled "flax seed oil"). The stuff used for paint is processed differently, but essentially the same. They are natural and non-toxic.

Actually, all linseed oil is processed the same. There is no difference between the purified linseed oil used for painting, and the flax seed oil from health food stores. Save for where it is packaged. The processed linseed oil is shipped from the refiners to a food certified (typically kosher) packaging. No further refining is done.

Boiled linseed oil isn't truely boiled either. It is either raw linseed oil or purified linseed oil, depending on manufactures specifications, which has steam bubbled through it. The product never has enough heat applied to it to actually boil. Complaints about boiled linseed oil are unsubstantiated. The real complaint belongs to finishes and paint mediums that have boiled linseed oil as a major constituent. The remainder consisting of alcohols, aldehydes, and metallic oxides. Most supposed health officials seem wave their ignorance of the difference as fact in the face of an uninformed (typically American) public. I also place some of the blame on the marketing companies, who persist in labeling these finishes and such as boiled linseed oil, and hiding the rest of the ingredients in the fine print.

Certainly there are people that are allergic to flax seed oil. Just as there are those allergic to walnut oil (I work with one), rape seed oil, olive oil, and peanut oil. However, most allergies related to oil painting are to true turpentine or to reactions to certain metallic pigments.

Andrew

Andrew
12-05-2005, 12:56 PM
So is it OK to use the flax-seed oil from a health food shop for painting?


It sure is! It is the same as the purified linseed oil sold in supply stores. I would check prices though. At the "health" food stores, it is a lot more expensive than ordering a quart through an art supply dealer. But prices may vary by demand and availability.

Andrew

Andrew
12-05-2005, 01:10 PM
No, striktly speaking, that's true.

But you don't need to be a genius to find info about this in of the many books on artist's materials. I quote from Ray Smith: "The oil is pressed from seeds. Modern oils are normally hotpressed. One can also buy coldpressed oil, which is considered as being of better quality."

Cold Pressed oil is crushed and extracted via alkali then the alkali is precipitated using acids. The final product is washed with water and seperated. Hot pressed oil is exposed to steam and crushed. Any extractants (like alkali) is used to seperated different oils or to clean impurities from the oil. This applies to all oil grains not just flax seed.

In Europe typically the first round of extraction is a cold press, This is where the raw linseed oil, from which purified (and food grade) linseed derived, is taken. Then the remnants are hot pressed, and this second extraction is for industrial use. Typically for polymers.

In North America, most processing plants use solely hot pressing. The raw linseed oil is graded and purified accordingly.

Andrew

Einion
12-06-2005, 04:28 AM
But you don't need to be a genius to find info about this in of the many books on artist's materials. What the books say isn't relevant to my point, my point was about what you brought up - the general quality - that you can't know with certainty with any material made from natural ingredients. You can do this online, although the impression is better in the flesh, compare the colour of different cold-pressed linseed oils - their properties will vary nearly as much as their colour :)

As far as the quote goes, after reading we then have to decide/judge if the source is reliable or not. Compare what four or five of the artists' handbooks currently in print say on the differences between, and advantages of, alkali-processed and cold-pressed linseed oil and you'll find some really odd anomalies.

So, if you buy artist's oil you know it's processed for artistical use. Do we? Which brands use oil processed specifically for use in artists materials Karin?

Since artistical oil isn't that expensive, I don't see the point in using food-store oil in painting mediums even if they sell drying-oils in food-stores.I would agree with this as a rule.


Actually, all linseed oil is processed the same. In what way?

Boiled linseed oil isn't truely boiled either.Are you saying that boiled linseed oil is made only by the method you described?

Complaints about boiled linseed oil are unsubstantiated.All of them? Nah ;)

However, most allergies related to oil painting are to true turpentine or to reactions to certain metallic pigments.Yep, turps is the most hazardous of the common ingredients in oil painting.

Cold Pressed oil is crushed and extracted via alkali then the alkali is precipitated using acids. The final product is washed with water and seperated. I believe you're mixing up two different processes here Andrew ;)

Einion

turlogh
12-06-2005, 04:58 AM
Do we? Which brands use oil processed specifically for use in artists materials Karin?
To the best of my knowledge, only Studio Products claims that their paint is made from a grade of oil specifically intended for painting. I don't know enough about the chemistry to understand the differences, although their oils and paints are excellent.

Beancrusher
12-06-2005, 08:33 AM
Alkali does not "extract" any oil, it is used in the refining process only.

There are ony two commercial facilities producing linseed oil in the U.S. One is operated by Cargill in North Dakota and the other by Archer Daniels Midland in Red Wing Minnesota. Both use very similar processes, that involve heat, pressure, and hexane to extract the oil. I have heard that there are cold-press facilities out there, but cannot confirm one way or another. The methodology would be very ineffecient in terms of oil extraction and thus economically unfeasible except for perhaps the art materials market. All companies today producing commercial and consuemer paint, stains, etc, use oil from one or both of these two plants. I can't speak for the artist materials market.

Today, without getting technical:
The flaxseed is heated and ground.
The ground seed is put through an expeller, a continous process creating extremely high pressure which removes aprox. 1\2 of the oil available in the flaxseed.
The expelled product is then put through flaking rolls to create very thin flakes.
The flakes are put through a series of hexane (a pertroleum solvent) washes in equipment called an extractor which removes the remaining oil.
The hexane is completely removed from the oil through distillation.
The two oils (expelled and extracted) are comingled as crude oil for refining from there. This crude oil will contain oil ( which are long chain fatty acids attached to a hydroxyl group), free (or unattached) fatty acids, and we'll just call it "junk".

Raw linseed oil goes through a water and acid wash in a very high speed centrifuge, which removes the junk that would gravity seperate on its own and some of the free fatty acids.

Boiled linseed oil is simply raw linseed oil with metallic driers added to it. (extremely small amounts are all that is needed)

Refined oil starts as crude and is but through the same type of high speed centrifuge, but instead of water and a little acid, caustic soda (thus the term alkali, which is used interchangably meaning a strong base) is the agent and it removes virtually all the free fatty acids and junk. To get the light, bright color, then this oil is bleached by mixing it with a bleaching clay and putting it through a cleaning press which removes the dark color bodies.

That is roughly how you get the "alkali refined" oil you see might see on the shelf, and this is the product used in inks, paints, stains, etc. For darker colored coatings and stains, they might start with raw oil for its cost advantages.

I am sure more than you wanted to know, but there you have it.

Andrew
12-06-2005, 11:22 AM
Are you saying that boiled linseed oil is made only by the method you described?

Yes. Speaking from experience. True "Boiled" linseed oil is raw (or occasionally purified) linseed oil that has steam bubbled through it until it attains a certain amber color and viscosity. Some companies mix in additives, such as sicatives, aldehydes, ketons, and alcohols and still sell it as boiled linseed oil, but that is deceptive. The linseed oil is only a carrier then. But that is a marketing and regulatory issue.

All of them? Nah ;)Einion
If it is true, unadulterated boilded linseed oil (which is what I by for my wood finishing) then it is safe. Save for the whole spontaneous combustion issue, and rag disposal. That doesn't change.



I believe you're mixing up two different processes here Andrew ;)

True cold pressing is merely a press and grind which squeezes out the oil and water. The two then are seperated via decantation. However, most industrial "cold pressing" actually combines forced steam into the process to steam distill the squeezings to obtain a purer product in a shorter time. Thus making a modified hot press rather than a cold press. In plants that use a true cold press, The decanted material is then treated with alkali to remove the unwanted fatty acids from the raw linseed oil. This process is called saponification, which gives glycerol, raw linseed oil, and soap. The three are seperated accordingly.

Hot pressed adds the pressurized steam during the grinding and mashing process and uses a continuous distillation process.

Some manufacturing processes use a solvent extraction to remove the oil from the unwanted fatty acids and protein matter. Solvents such as hexane, cyclohexane, etc. depending on the source grain, are then removed via distillation.

There are ony two commercial facilities producing linseed oil in the U.S. One is operated by Cargill in North Dakota and the other by Archer Daniels Midland in Red Wing Minnesota. Both use very similar processes, that involve heat, pressure, and hexane to extract the oil. I have heard that there are cold-press facilities out there, but cannot confirm one way or another. The methodology would be very ineffecient in terms of oil extraction and thus economically unfeasible except for perhaps the art materials market. All companies today producing commercial and consuemer paint, stains, etc, use oil from one or both of these two plants. I can't speak for the artist materials market.

There is also a Spencer-Kellogg (formerly Nat'l lead) plant in Minneapolis. I know the ADM plant markets bulk material to food facilities. I can't say if Cargill does, but I would suspect that they do. The Kellogg plant only deals with the paint and polymer industry. Most of their product went to artist paint's manufactured in the US, Canada and Mexico.

Otherwise you most dead on. From what I recall from my last agricultural chemistry seminar, the post centrifuge material is commonly referred to crude linseed oil. Alkali treatment and washing, which still leaves a darker oil is raw linseed oil, and the second run and bleaching gives the purified oil we all know and love. But that really shows more how marketing and customer desires drive manufacturing process and nomenclature.

Watch the use of "boiled" though. If you talk to a linseed oil chemist or engineer (or even a wood finisher) it is just steam treated linseed oil. Marketing is another matter. I don't quite understand why they feel the need to add driers to it anyway. The steam treatment jumpstarts the polymerization (drying) process enough on it's own. The driers can't add that much to it anyway.

Andrew

georgeoh
12-06-2005, 02:04 PM
Cargill and Archer Daniels Midland (ADM) are the two major processors of linseed oil today in North America, but there are a few other companies who also produce linseed oil. Most linseed oil today for industrial application is produced using the hot expeller and solvent extraction methods. It is not economically feasible to produce it otherwise. Cold-pressed linseed oil is produced for the human consumption market and not the artist market, although a small amount finds its way there.

Linseed oil for artists' use is not toxic, except that it may produce allergic reactions in some people. This does not mean it is safe for human or animal consumption and I do not think anyone was asking about that usage.

A Note on the Toxicity of Artists' Materials
All these questions about toxicity almost seems to be directed at consuming these products, which artists' materials were never intended. Sometimes artists' materials cannot be made non-hazardous, because they are necessary for certain creative activities. When used in properly supervised and controlled conditions, they can be employed with the risk of exposure to potentially hazardous materials greatly minimized. You must remember, however, that you are dealing with materials that may be harmful if not handled with care. It must not be assumed that the absence of a health warning indicates that a material is safe. They can be harmful and persistent exposure to them will at least cause irritation. There is an increasing amount of information available as to their dangers, but the safest way is to treat all materials as potentially harmful.

Do not let these warnings, however, deter you from using these materials, since the minimum care needed for most materials is no more than good sound studio practice, which every responsible artist should do.

tk04
12-06-2005, 06:56 PM
I find info from people with first-hand experience of different remedies used in painting, valuable. That said - this is about painting. The oil used in paintings is the most important factor to determine, among other things, the yellowing. (Please, Einion, if you want to twist this statement, what about starting a thread called - What causes yellowing in painting?). Since I know that the oil I buy from producers of artistical materials are up to an acceptable standard, I wouldn't buy oil, meant for mediums, in a food-store.

As for that, I really doubt that food-store linseed oil is identical to good quality linseed oil sold as artist's materials, principles for processing aside. But that's not the main point. The main point is that I know what I get when I use oil sold by producers of artist's materials. I would even pay a dollar more for the litre, with open eyes, to get oil with a quality quarantee.

Beancrusher
12-06-2005, 08:28 PM
Am curious Andrew where you aquire your "boiled" linseed oil. Who is the actual manufacturer? Certainly "boiled" is a misnomer today, but that has been true for probably at least the last 100 years. It isn't a new thing, no one is being deceptive, because all in the industry understand what it is. There are ASTM standards for it in regards to drying time, viscosity, color, iodine value, etc.

The "Spencer Kellogg" facility in Minneapolis hasn't operated for many years now. Spencer hasn't actually crushed any flaxseed for probably over 25 years or so at least. They used to buy all their base oil from the Honeymead plant in Fridley, Minnesota (northern suburb of Minneapolis)when the discontinued their own crushing, and then they bought it all from ADM when the Fridley plant closed, (I think by then they were Nat'l Lead), but they were subsequently purchased by Reichold Chemical, who themselves where bought by DIC (Dainippon Ink and Chemicals), but have just this year underwent an executive buyout by their upper management team.

ADM markets NO linseed oil to food manufacturers. Linseed oil does not have USDA or FDA approval as an edible oil. Every bill of lading on every shipment from Cargill and ADM will state clearly that it is for industrial use only. Linseed oil finds its way into the health food stores because it sort of "flies under the radar" and the quantities and consumption aren't high enough to be an issue. Also, it is non-toxic so not an issue, except perhaps as noted for those with a specific allergy. The same chemistry that makes it a good drying oil, makes a terrible edible oil. Some eastern european countries will however actually blend it in very small quantities into their margarine blends if it is cost effective to do so. (or least they used to, not sure anymore)

Einion
12-07-2005, 08:10 AM
Are you saying that boiled linseed oil is made only by the method you described?Yes. Speaking from experience. What about heating to ~200C for a number of hours? After which a metallic drier or combo of driers may be added to make what is sometimes referred to as linseed oil varnish.

True "Boiled" linseed oil is raw (or occasionally purified) linseed oil that has steam bubbled through it...I hope this isn't a No True Scotsman thing! :D

...until it attains a certain amber color and viscosity.I've seen a cold-pressed oil that was darker than this! :) (Swedish, from Kremer, on sale in London in case anyone wants details.) Of course it depends on the volume one is looking through what colour an oil appears, the Swedish oil above was in a 500ml container I think, anyone who buys oil from Kremer will know the shape of the plastic bottles they use (~10cm deep?)

True cold pressing is merely a press and grind which squeezes out the oil and water. Exactly, that was my point.

Real cold-pressed oil is just what the name implies: think extra-virgin olive oil.

In plants that use a true cold press, The decanted material is then treated with alkali to remove the unwanted fatty acids from the raw linseed oil. I think you're mistaken. This would an alkali-processed oil, which would defeat the whole purpose of cold pressing. This may be used for a cold-pressed oil as per a commercial definition (extracted as you describe earlier) but AFAIK it's usual to use two other methods to remove the foots.

So I hardly think it's accurate to say all linseed oil is processed the same do you? ;)

Einion

Einion
12-07-2005, 08:13 AM
Please, Einion, if you want to twist this statement...I didn't twist anything above Karin. As we saw the other day perhaps you're just not reading carefully enough.

Could you answer the question I posed above please - which brands of oil paint use oil processed specifically for use in artists materials? You stated "if you buy artist's oil you know it's processed for artistical use." so, is this based on some evidence or is it merely supposition?

Einion

Andrew
12-07-2005, 10:34 AM
Am curious Andrew where you aquire your "boiled" linseed oil. Who is the actual manufacturer? Certainly "boiled" is a misnomer today, but that has been true for probably at least the last 100 years. It isn't a new thing, no one is being deceptive, because all in the industry understand what it is. There are ASTM standards for it in regards to drying time, viscosity, color, iodine value, etc.

I will have to dig some out and look. I just pick it up at my local True Value hardware store. It just 100% linseed oil as the contents. Personally, I mix it with a wee bit of isopropanol, and rub it into some of the damaged wood around my house. The same label manufactures one with cobalt drier added too. I haven't ever purchased it however.

The "Spencer Kellogg" facility in Minneapolis hasn't operated for many years now. Spencer hasn't actually crushed any flaxseed for probably over 25 years or so at least. They used to buy all their base oil from the Honeymead plant in Fridley, Minnesota (northern suburb of Minneapolis)when the discontinued their own crushing, and then they bought it all from ADM when the Fridley plant closed, (I think by then they were Nat'l Lead), but they were subsequently purchased by Reichold Chemical, who themselves where bought by DIC (Dainippon Ink and Chemicals), but have just this year underwent an executive buyout by their upper management team.

It can't have been that many years. It hasn't been that many years since my father worked there. They were still getting some flaxseed in when he started. But were purchasing much form Honeymead and ADM (Red Wing I think). My father was still there when Riechold purchased, but had left before DIC.

ADM markets NO linseed oil to food manufacturers. Linseed oil does not have USDA or FDA approval as an edible oil. Every bill of lading on every shipment from Cargill and ADM will state clearly that it is for industrial use only. Linseed oil finds its way into the health food stores because it sort of "flies under the radar" and the quantities and consumption aren't high enough to be an issue. Also, it is non-toxic so not an issue, except perhaps as noted for those with a specific allergy. The same chemistry that makes it a good drying oil, makes a terrible edible oil. Some eastern european countries will however actually blend it in very small quantities into their margarine blends if it is cost effective to do so. (or least they used to, not sure anymore)

Possibly in the US, there are standards for food grade linseed in the US, but it is an unpopular food oil. We work with food grade palm and canola oil in an extension of our plant here. And just finished reviewing all the oil specs. Linseed oil is even on the Rabbi's list for kosher edible oils. I used worked for ADM as a dispatcher and used to route rail cars to Canada (what they did with it was out of my keen) but it had a "food grade" tag. It wasn't often, as we handled crude and refined soy oil, but occassionally they would tack on a car or two to a rail run. I would hazard a reasonable assumption that Cargill does the same.

I think you're mistaken. This would an alkali-processed oil, which would defeat the whole purpose of cold pressing. This may be used for a cold-pressed oil as per a commercial definition (extracted as you describe earlier) but AFAIK it's usual to use two other methods to remove the foots.

So I hardly think it's accurate to say all linseed oil is processed the same do you?

I should have said sometimes treated with alkali. The process of removing the junk varies from plant to plant. Depending what was in vogue (engineeringly speaking) and what was commercially feasible. Like all things trends change. It may be moot in a few years anyway. It is getting harder and harder to get cold pressed oil. Hot pressed gives higher and cleaner yields, making it more and more industrially preferred.

Andrew


Andrew

tk04
12-08-2005, 07:55 AM
I didn't twist anything above Karin. As we saw the other day perhaps you're just not reading carefully enough.

Could you answer the question I posed above please - which brands of oil paint use oil processed specifically for use in artists materials? You stated "if you buy artist's oil you know it's processed for artistical use." so, is this based on some evidence or is it merely supposition?

Einion

The oils used in mediums and paint in fine art painting, is the single most important factor to determine, among other things, how the paint will yellow over time. Since I know that the oil sold by producers of painting materials has a certain acceptable quality, I would not buy oil from hardware-store, food-stores or other places, sold for other purposes than fine art, if I am to use it as a painting medium. The oil is too important to fuss with.

Of course, if one doesn't bother about yellowing, or other properties of the oil, there is a lot of different liquids to mix into a painting, some of them sold in food-stores.

This was a comment to the general discussion in this thread. One of the posters in this thread has recommended the use of linseed from other sources than fine art paint manufacurers for use as a paint medium or as oil for making paint. He is wrong about that, imo, but I tried to say this in a polite manner, not to insult or attack in any way. The above mentioned poster has contributed to this thread in other valuable manners, and of course he doesn't mean to say something misleading or alike.

Normally, linseed oil isn't sold in food-stores. So yes, it's an assumption, that most of the produced linseed-oil is processed for house-painting, wood-work and artist's material, or alike.