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The Process of Alkali Refining Linseed Oil

21 thoughts on “The Process of Alkali Refining Linseed Oil”

  1. I never knew the process was so complex and had so many steps,

    What’s involved to produce Cold Pressed Linseed oil?

    Thanks

    Reply
    • Hello Mark,
      We learn a lot from researching these articles too, including how complicated industrial processes can be! Another interesting point that wasn’t mentioned in the article, is that the artist materials industry uses only a small fraction of the oils produced for food, the coatings industry or for other industrial uses.

      Regarding cold pressed oil, it also goes through a number of steps without the use of chemicals or heat. The seeds and oil must be kept below around 100 degrees F in order to be classified as cold pressed. The seed is pressed without steam which produces less oil with less impurities. Because pressure creates heat, the presses can be cooled. The oil is captured under a blanket of nitrogen to keep the oil fresh and so it does not oxidize. The oil can be washed with water and/or clay, filtered and centrifuged. They might also winterize the oil, which cools it to the point when the waxes in the oil solidify and drop out.
      Thanks!

      Reply
  2. I agree that you have broken down a very complex process so a non chemist can understand. It really made me understand the difference between this product and cold pressed oil and the advantages in preparing paint and using as an additive. Thank you. I am sharing this with my students. Bravo

    Reply
    • Hello Kristine,
      Thank you for your comment and for sharing this article with your students! We are glad you found it helpful!
      Best Wishes,
      Greg

      Reply
  3. Linseed oil has been recommended to stabilize plywood woodblocks for Japanese style carving and printing. One source mentions “activated linseed oil.” Is that simply boiled linseed oil? Further can you comment on drying times? One source says it takes several days and another says about a single day. Thanks very much.

    Reply
  4. Hello Jawed,
    Unfortunately, we do not have specific information about different presses and the pressure or temperature they produce. There are standard requirements for keeping the seed under a certain temperature (~100F) in order to label the oil product “cold pressed”, but for heat and steam pressing, the heat and pressure used to extract the oil seem to be determined by the type of press and the desired end use for the extracted oil. Perhaps you can contact a seed press manufacturer an inquire about the specs of their machines.
    We wish you the best in your research.
    Greg

    Reply
    • Hello Sir,
      We are not sure if these terms can be used interchangeably. It appears break-free oil has been cleaned to some extent, perhaps with an acidic solution only. This is to remove the “break” or gums, also called mucilage, from the oil. Removing these impurities allows the oil to be heated without “breaking” or becoming cloudy and clotted. Oils that are heated in this way are typically used for varnishes. Alkali refined linseed oil has likely been through a more vigorous cleaning process than break-free oil.
      We hope this helps.
      Greg Watson

      Reply
  5. Hi we are a paint manufacturing company & for testing of incoming pigments & extenders we need acid refined linseed oil with an acid value of 5-7 mg KOH/gm of sample. This test is as per ISO 787 specification. Can you please suggest?

    Reply
    • Hello John,
      There are a number of larger linseed oil manufacturers who provide oils with varying acid values. We do not disclose our manufacturer, but quick internet search should turn up several results.
      Take care,
      Greg

      Reply
    • Hello Tu,
      The free-fatty acids that are removed during alkali refining are not part of the triglyceride structure which primarily forms the film. Free fatty acids are washed out of the oil as a soap and then collected, cleaned and replaced back into the oil at varying levels. The levels depend on the needs of the end user. Free fatty acids can help wet pigments, so it is thought cold pressed oil is beneficial for that purpose. Otherwise, it seems from our research and in-house testing that Alkali Refined oil and cold-pressed are on par in terms of film formation and long term durability. Plus, the longevity of an oil paint layer is so dependent on the pigments used, that is difficult to disconnect the two in any real life study.
      Please get in touch with any additional questions. [email protected]
      Greg

      Reply
    • Hello Andrew,
      Not sure any of the drying oils wouldn’t have some level of acidity. Unfortunately, cannot think of any alternatives to hide glues, acrylics or PVAs for sizing fabrics. You could try a polyester fabric, which wouldn’t degrade with oil contact. But again, you would be using synthetic materials.
      We will certainly keep our eye out for effective alternatives and let you know when we find something!
      Take care
      Greg

      Reply
      • HI Warren,
        sorry for the delay in response…thanks for your comment. We have not tested starches as sizing. But an interesting idea and perhaps something to be tested.
        Best Wishes,
        Greg

        Reply
  6. Hello

    Williamsburg Cold pressed linseed oil is described on the web as „Less processed than alkali-refined.“ Does that „Less processed“ mean, that it is processed to certain degree, but not as much as alkali refined?

    For example Schmincke offers cold pressed linseed oil, described as „Natural, mucilage-free linseed oil from first pressing,“ (https://www.schmincke.de/en/products/mediums/oil-mediums/linseed-oil-cold-pressed.html) and Kremer pigmente offers cold pressed linseed oil from Sweden, described as „Linseed oil from Sweden, cold-pressed and filtered“ (https://www.kremer-pigmente.com/elements/resources/products/files/73020-73600_Oils.pdf). When I asked Kremer pigmente about the „filtered“ part, I was told that it is cold pressed and cleansed from mucilage by letting it settle, but not treated any further.

    Is Williamsburg cold pressed linseed also at least filtered, i.e. without mucilage?

    By the way, pity that Williamsburg doesn’t make Sun thickened linseed oil any more (although I know, that there are few other sources).

    Regards
    Ivan

    Reply
    • Hi Ivan,
      Oil manufacturers can be somewhat reluctant to detail their process point by point. What we have discussed with our provider is that cold pressed oil is extracted without heat or solvent and then winterized and filtered. Winterization and filtering removes waxes and then colorants, plant matter and mucilage respectively. Sorry about the sun thickened oil. Perhaps you can make your own during the summer months!
      Take care,
      Greg

      Reply
  7. Thank you so much for a totally comprehensible article. I thoroughly enjoyed reading it. If I was to set about making paints using a three roll mill, is this alkali-refined oil the best choice? If not, what type of linseed oil would you recommend? If I was going to mix in some walnut oil, which kind of walnut oil do you recommend? If there are different kinds. Thanks so much for writing articles like this.
    Warmly, David

    Reply
    • Hi David,
      Thank you for your comment. Yes, you can use Williamsburg alkali refined linseed oil to make your oil colors. That is what we use for our paints. The cold-pressed oil will work also. As for walnut oil, you may be able to find refined walnut oil in the art supply shops, but if not, you can try Kremer Pigments. They have a refined Walnut oil: https://shop.kremerpigments.com/us/shop/mediums-binders-glues/73500-walnut-oil-refined.html
      The walnut oil in food stores may contain anti-oxidants to help with freshness. While this shouldn’t harm the paint, it may slow drying of your oil colors and might not be preferable.
      Hope it goes well!
      Greg

      Reply

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