Skin forming in oil paints in jars

I am used to painting out of plastic jars with acrylics already mixed to my preferred consistency. However, now,I am switching to oils. Several weeks ago, I mixed my oils from tubes into plastic paint jars and added Odorless Mineral Spirits to get the right consistency. I like to paint in a very expressionist way and don't want to stop to mix paints. I am happy to have the paints dry in 24 hours. Then much to my  dismay most of the colours developed a skin in the jars. THEN  I  discovered your website and how you mix your paints from tubes into Mason jars to get the right consistency for your painting with your own special medium mix. So, I am wondering if I just added more linseed oil, or safflower oil, depending on the original mix in the oil paint, whether that would help prevent the drying in the jar, but still allow me work freely with a consistency I like and not take too long to dry. I suspect that your medium might take longer to dry than I would like, but I could not find any mention of it on your video. Other, than that, it was suggested, I drop in a little water on top to prevent the coating forming before I finish up a painting session, or turn the jars upside down to prevent the skin from forming. 

Any suggestions would be most welcome. 



  • Sophia

    Welcome to the DMP Forum.

    The clove oil and Venetian turpentine (really a resin) are the ingredients slowing down skin formation.

    Using Mark's slow dry medium allows me to keep oil paint fresh and useable for at least two years. In well sealed, small glass jars, minimising the air space. On the canvas the earth tones are touch dry in a few days and the lights in a week or ten days depending on temperature and humidity.

    Oxygen is the element that starts to set up the polymer molecules in paint, once the volatiles vent off.

  • Couple of things, it may be the plastic jars, most plastics will not stop solvents like odourless mineral spirits from escaping.  But in addition to that fast drying paints with no clove oil will form a skin unless you have very special lids that form a gas seal to prevent solvent from escaping.
  • SummerSummer -
    edited November 2015


    Mark recommends his SDM be used with Winsor & Newton Artists' Oil Colours and I personally haven't tried his recipes with other brands. Maybe someone else can weigh in here about that. To start with, you will have to know how much OMS you have already added to your paints in the jars so that you can add the following in their proper proportions--just in case you are interested:

    Slow Dry Medium (SDM) for Winsor & Newton Artists' Oil Colours (37ml tubes):

    • 10 parts odorless mineral spirits (Any artist-grade odorless mineral spirits will do.)
    • 5 parts stand oil or linseed stand oil (This is not the same as refined linseed oil.)
    • 1 part refined linseed oil
    • 5 parts Venice turpentine
    • 2 parts 100% Oil of Cloves

    For burnt umber use the above SDM recipe plus 3 teaspoons of 100% Oil of Cloves liquid for every 37ml tube. This will give you equal drying time with all the other colours that you mixing.

    for titanium white only:
    • 10 parts OMS

    • 5 parts refined linseed oil

    • 5 parts Venice turpentine

    • 1 part stand oil

    Glass Mason jars, with their rubber lid seals (air tight as Mark recommends) are best. Summer

  • @Summer You left out the clove oil in the main recipe and also, for burnt umber, it's 3tsp of clove oil per 37ml tube of burnt umber. I don't think Sophia wants to use Mark's medium, but just in case someone stumbles upon this thread I want to make sure they don't get confused about the recipes or application. Here is the up-to-date info on medium recipes which also has a link to a video with more detailed instructions and other information (like storing jars in the fridge, etc):
  • SummerSummer -
    edited November 2015
    Thanks David.  Checked my stash of bottles of SDM and they have all of the proper ingredients and proportions.  At least I got it right there!  Thanks again.  Summer
  • @SophiaI think you have to displace the air in the jar somehow. Inert gases work well. But, who has that lying around? And then you would need a container with a good seal. It seems impossible to paint with out creating some waste. Maybe just mix from the tube in the amounts you want to paint with. It's tedious but will cut down on waste. Good luck to you!

    It works with Gamblin oils as well :)
  • I read about adding glass marbles to displace the air in containers.  I think @dencal may have some experience with this.
  • Summer

    Yep, I use glass marbles to displace the air. Works fine. Started using marbles back in June this year with water mixable W&N Artisan paint and standard SDM, stored in good quality Decor snap caps. Six months in they are essentially the same as the day I mixed the paint.


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